INTRODUCTION OF SIGNAL TRANSDUCTION & DRUG DISCOVERY

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INTRODUCTION OF SIGNAL TRANSDUCTION & DRUG DISCOVERY

訊息傳遞與藥物開發概論

評分標準：出席: 20%

期中考: 40%

期末考: 40%

Wen Zhi-Hong PhD.

海B4018 分機5038

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人生目的不外乎「生得好，老的慢，病得輕，死得安」

Birth生 Aging 老 Sickness 病 Death 死 Joy 喜 Anger 怒 Sorrow 哀 Happiness 樂

Protein

RNA

Genotype

DNA

Phenotype 我要藥

4

Global Pharmaceutical Market

90b 10

Others

55b 6

Non specific inflammation

55b 6

Hematology

80b 9

Respiratory

100b 11

Gastrointestinal

110b 12

Infection

170b 19

Cardiovascular

150b 17

Central nervous system

60b 7

Cancer

$$$$

% Disease

2008年全球藥品市場約7700億美元，其中神經性疾病的用藥 約1180億美元佔15.3%，而癌症用藥約700億美金只佔9

%(Maggon, 2009)

(2)

5 6

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Global Biotechnology Market 2006-2008 ($ billion)

8

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世界人口數、醫療保健支出與營養產品銷售概況

1995 2000 2005 2010e

全球人口總數(百萬人) 5,683 6,076 6,445 6,815

65歲以上人口數(百萬人) 373 423 477 528

全球醫療保健支出(億美元) 28,750 39,050 55,400 77,100

平均每人醫療保健支出(美元) 506 643 860 1,131

營養產品銷售(億美元) 784 1,063 1,450 1,966

平均每人購買營養產品支出(美元) 13.8 17.5 22.5 28.8

資料來源：聯合國人口司(UNPD)、世界經濟合作發展組織(OECD)、The Freedonia Group, 2006；台灣經濟研究院生物科技產業研究中心整理

10 163 3700 6000

1923 1097 600

製藥廠家數

0.60%

8.9%

1.2%

佔全球藥品市場％

70%

17%

57.3%

學名藥佔處方藥比例

1%

13%

學名藥市場成長率

8 70

247 學名藥市場（億美元）

119 13 8.4

522 150 820

平均每人藥品支出（美元）

4%

17.5%

8%

10.2%

9.1%

藥品市場成長率％

126 32 104

665 100 3,491

藥品市場（億美元）

26.7%

22.6%

18.0%

25.6%

16.4%

藥品占醫療保健支出％

6.4%

4.7%

4.4%

9.6%

7.8%

16.1%

醫療費用佔GDP

16,471 1,970 700

34,252 18,370 45,520

GDP(美元)

0.23 13145 10.953

1.28 0.488 3.024

人口（億）

台灣中國大陸印度

日本韓國

美國 2006年

重要指標各國比較表

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2006年全球藥品市場成長率

17.5%

印度

12.3%

中國大陸

10.5%

非洲

11%

10.5%

亞洲（日本除外）

6%

12.7%

拉丁美洲

9%

0.5%

日本

29%

4.4%

歐洲

45%

8.3%

北美

佔率成長率

地區別

IMS Health 預測2007年全球藥品市場達到6700億美元，成長率約6

％，學名藥675億美元；成長率16.8％，預估2010年達到1213億美元。

2006年全球製藥業成長的部分27％來自國民所得2萬美元以下的區域 2006年全球藥品市場排名依序美國、日本、法國、義大利、英國、

西班牙、加拿大、中國及巴西

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生技鑽石起飛方案

(4)

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生技與製藥產業之主要成員

政府律師與會計

師事務所

承銷商、銀行與創投公司生技與製

藥公司

生技與製藥產業醫院暨健保

系統

大學與研究機構

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2007~2009年生技人才需求

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廣義生物科技領域

健康食品動物用添加劑生技食品

GMO(gene modified org.) 基因轉殖動物,花卉藥用植物農業,動物生技

生物性觸媒生物性環境檢測微生物製劑生物環保

其他

Health care manegement HIS-hospital inf. system RIS-radiology LIS-- laboratory Gerontechnology E-health

Pre-clinical動物試驗 Clinical trials人體試驗 CRO(contract research org.)

Diagnostics 醫療/生技服務

醫藥中間體原料藥學名藥新劑型藥物傳輸系統中草藥,科學化中藥疫苗

新藥研發(含孤兒藥) 基因治療製藥,治療藥物

Lab-on-chip Microarrays 生物晶片( Biochips)

DNA sequencing Genomics

BioComputer 生物資訊 Bioinformatics 生物晶片( Biochips) 生物資訊( Bioinformatics)

醫療儀器血液製劑醫療材料檢驗試劑醫療儀器,材料,試劑廣義的生物科技

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Value vs. Volume

基因治療

分子診斷

生醫光電

組織工程蛋白質學

新藥標的

生物晶片

生物資訊

疫苗

新藥

新醫材

新試劑

種苗花卉

醫療器材檢驗試劑

原料藥學名藥

生技食品工業酵素

高

低

小經濟產值大

附加價值

(5)

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不同年代生物科技的發展與相關的生技公司類型

1.Array Biopharma 2.Dendreon 3.Rigel 4.捷容(Geron) 人類基因組計劃完

成;蛋白質體學研究開始;新醫療技術新藥探索、高速新藥篩

選、蛋白質晶片、

再生醫學 2001~

1.賽雷拉 2.人類基因科學 3.英賽特(Incyte) 4.艾菲矩陣人類基因組計劃開

始;基因定序基因體、功能基因體、

生物資訊、

基因晶片 1991~2000

1.基因科技 2.安進以蛋白質工程技術

製造蛋白質藥物重組DNA蛋白質

1981~1990

相關的生技公司主流生物技術

主流生技公司類型年代

18 資料來源:生技醫藥產業發展歷程與趨勢,林衛理博士,2005.03

何謂生物科技??

19 20

Discovering and Developing the ‘One Drug’

Source: FDA Website

compounds

laboratory

Average: 15 years Cost: 270億台幣

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Drugs and Leading Drug from natural products

WHO estimates that

~80%

of the world’s population use

traditional medicine.

>41% of new approved drugs had natural

products

as their source.

David J. Newman, et al. Nat. Prod.

Rep., 2000, 17, 215-234 Gordon M. Cragg, et al. J. Nat. Prod.,

1997, 60, 52-60

6%

26%

9%

59%

Synthetic Drugs (全合成)

Modified Natural Product Drugs (天然物修飾) Natural Product Drugs (天然物)

Synthetic Drugs Based on Natural Product Models (以天然物為基礎 合成得到)

但超過80%原始和天然物有關

絶大部份的藥物及前驅藥物都源自於天然物

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典型,或按照科學方法之藥物開發流程 Classic, rational approach to drug discovery

Therapeutic concept

Efficacy Assay (HTS)

Screen compounds

In vitro models

In vivo Pharmaco-

dynamics

Toxicology

NDA submission New drug

launch Preclinical Development

compound

patent analytical production

Pharmaco kinetics

Phase 1 Clinical study Phase 2

Clinical study Phase 3

Clinical study

n-th NCE First NCE, iterate Evolve SAR and MC concepts

IND Clinical

Development compound

HTS: High-throughput screening IND: Investigation new drug NCE: New chemical entities NDA: New drug application Structural-Activity Relationship

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Accelerated ^discovery based on indigenous or traditional knowledge of medicinal plants

IK provides lead for therapeutic

concept

Efficacy Assay (HTS)

Screen compounds

In vitro models

In vivo Pharmaco-

dynamics

Toxicology

NDA submission New drug

launch Preclinical Development

compound

patent analytical production

Pharmaco kinetics

Phase 1 Clinical study Phase 2

Clinical study Phase 3

Clinical study

n-th NCE First NCE, iterate Evolve SAR and MC concepts

IND

Clinical Development

compound

以民間(或土著)知識運用為基礎可以加速藥物開發之時間

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Introduction

Signal transduction overview Chemical signal

Receptor

G-protein coupled receptor ion channel

enzyme-linked receptor Small G protein

Phosphorylation/dephorylation Phospholipase and Ca2+

Oxidative stress and inflammation General pharmacology

Disease vs. mechanism Drug discovery

process

model

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Mapping of the human genome

• Pr. Februar 2001: 32-39000 genes

• Of which 20% implicated in cell signalling:

– 3000 genes involved in regulation of gene expression

– 1800 genes involved in signal pathways (including

>600 kinases, >200 phosphatases) – 1300 genes involved in

cell-cell communication

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細胞信號轉導大事記

‧1955年，Sutherland，cAMP第二信使學說，獲 1971年 Nobel Prize 生理和醫學獎

‧1963年， cGMP作為胞內信使的發現

‧1978年，Rasmussen，Ca2+第二信使學說

‧1983年，IP3和DG作為胞內信使的發現

‧80年代，Gilman和Rodbell，G蛋白的研究，獲 1994年 Nobel Prize 生理和醫學獎

‧80-90年代，酪氨酸蛋白激與信號轉導的研究

Signal transduction vs. Nobel Prize

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The Nobel Prize in Physiology and Medicine 1992

Eldwin G. Krebs Edmond H. Fischer

USA USA

1920-

(born in Shanghai, China) 1918-

"for their discovery of concerning reversible protein phosphorylation as a biological regulatory mechanism"

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The Nobel Prize in Physiology and Medicine 1994

Alfred G. Gilman Martin Rodbell

USA USA

1941- 1925-1998

"for their discovery of G-proteinsand the role of these proteins in signal transduction in cells"

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31 32

drug Targets

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２００３年台灣地區各類用藥銷售額 (1)

1.4 1,358

中樞及周圍血管用藥 15

1.4 1,748

長春花生物鹼 14

1.9 1,766

抗憂鬱劑 13

1.9 1,829

廣效盤尼西林抗生素 12

1.9 1,887

治療脹氣制酸劑 11

2.0 1,919

ACE抑制劑 10

2.0 2,115

ß-block阻斷劑 9

2.2 2,653

抗精神病用藥 8

2.8 2,723

抗潰瘍用藥 7

2.9 2,814

Angiotens-II拮抗劑 6

3.0 6,473

降血脂用藥 5

3.7 3,473

非類固醇抗風濕性關節痛 4

3.8 3,562

頭孢菌素類抗生素 3

4.1 3,859

口服降血醣用藥 2

4.8 4,523

鈣離子拮抗劑 1

市場佔有率

（％）

銷售額（萬元）

2003年

藥品類別

資料來源：

資料來源：IMS TAIWANIMS TAIWAN；；生技中心生技中心ITISITIS計畫整理計畫整理

34 1.3 1,284

非類固醇止痛藥 16

1.3 1,202

氟化奎諾環抗生素 17

1.2 1,110

抗癲癇製劑 18

1.2 1,099

止咳劑 19

1.0 保肝劑 893

30

1.0 鎮靜安眠製劑 902

29

1.0 代謝拮抗劑 917

28

1.0 其他抗癌用藥 925

27

1.0 紅黴素類製劑 957

26

1.0 抗組織胺用藥 960

25

1.0 怯痰劑 973

24

1.1 蛋白質製劑 999

23

1.1 1,018

鎮定劑 22

1.1 1,030

感冒製劑 21

1.2 1,080

血小板凝集抑制劑 20

市場佔有率

（％）

2003年

藥品類別

２００３年台灣地區各類用藥銷售額 (2)

資料來源：

資料來源：IMS TAIWANIMS TAIWAN；生技；生技中心中心ITISITIS計畫整理計畫整理

35 2003年

藥品類別市場佔有率

（％）

0.8 緩瀉劑 703

40

0.8 抗怕金森製劑 714

39

0.8 肌肉鬆弛劑 754

38

0.9 815

BETA2-刺激劑 37

0.9 免疫增強劑 817

36

0.9 抗高血壓製劑 829

35

0.9 其他抗生素 848

34

0.9 其他泌尿科製劑 868

33

0.9 凝血劑 874

32

0.9 其他盤尼西林類抗生素 878

31

２００３年台灣地區各類用藥銷售額 (3)

資料來源：

36

• 2003~2004年台灣地區藥品前二十名銷售排行

TARGOCID 19

ADALATOROS 19

ZOCOR 17 RISPERDAL

17

RISPERDAL 16

TARGOCID 16

PLENDIL 18

STILNOX 18

ZYPREXA 20

CELEBREX 20

產品排名

NORVASC 1

DIOVAN 2

LIPITOR 3

COZAAR 3

COZAAR 4

LIPITOR 4

VIAGRA 15 AMARYL

15

TAXOTERE 14

AUGMENTIN 14

APROVEL 13

ZYPREXA 13

REDUCTIL 12

PLAVIX 12

CELEBREX 11

RECORMON 11

DILATREND 10

ZOCOR 10

AUGMENTIN 9

VIAGRA 9

AMARYL 8

DILATREND 8

CIPROXIN 7

PLENDIL 7

PLENDIL 6

CIPROXIN 6

AVANDIA 5

產品排名

2004年 2003年

資料來源：

Anit-hypertension 得安穩 (全球第一) 血管收縮素Ⅱ拮抗劑提高患者的胰島素感受治療高血壓、心絞痛強效的抗生素,對組織穿透性良好非胰島素依賴型(第2型)糖尿病

抗生素抗高血壓製劑

諾美婷

Anit-hypertension 歐洲紫杉醇

精神分裂症降胆固醇藥 Anit-hypertension

抗生素嚴重、慢性精神

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暢銷藥物專利到期

公司產品主要適應症 2005年銷售額專利到期

Pfizer

Zoloft 憂鬱症 33 2006

Norvasc 高血壓 47 2007

Zithromax and Zmax 細菌感染 20 2006

Lipitor 降膽固醇 130 2010

Zyrtec/Cirrus 過敏性鼻炎 23 2007

Merck & Co. Zocor 降膽固醇 44 2006

Fosamax 骨質疏鬆症 32 2008

Astra-Zeneca Nexium 胃潰瘍 46 2005

Toprol-XL/Seloken 高血壓 17 2007

Eli Lilly Zyprexa 精神分裂症 42 2011

Glaxo-Smith Kline

Flonase/Flixonase 過敏性鼻炎 12 2006

Coreg 高血壓 10 2007

Advair/Seretide 氣喘 55 2008

Lamictal 癲癇 15 2008

Lmitrex/Imigran 偏頭痛 13 2008

Bristol-Myers Squibb Pravachol 降膽固醇 23 2006

Plavix/Iscover 動脈硬化症 63 2011

Novartis Lotrel 高血壓 11 2007

Sanofi-Aventis

Ambien/Stilnox 失眠 19 2006

Lovenox/Clexane 血栓 27 2006

Allegra/Telfast 過敏性鼻炎 17 2006

*

*億元美金

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What is signal transduction ?

Why signal-transduction play an important role of drug discovery ?

Signal → receptor → response → physiological function Signal → receptor → response → diseases

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Drug Discovery

Biological Projects from academia,

government,

biotech and pharma Assays

Proteomics Cell & Animal Models

Cell & Animal Systems Genomics

Toxicological Testing Phase 1 Clinicals Drug Development

Bioinformatics

Target Identification & Validation Phase

High Throughput Screening, Medicinal Chemistry, Computation and Protein Phase

Licensing, Co-Development, Pharma Partner Phase Medicinal HTS

Chemistry

CompoundsLead

Validated Target

Computer Modeling

Protein Structure Protein

Production

Software ^{Cell &}

Animal Models

Diagnostics

Drug Candidates

}

Compound Library

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A time line of some of the major findings in cell signalling

One of the most important aspects of modern

biochemistry and cell biology.

All cells must have the ability to detect the presence of extracellular molecules and conditions, and must also be able to instigate (慫恿) a range of intracellular response.

Single cell: signaling system enough complex; But multi- cellular organism has to coordinate the function.

植物的荷爾蒙

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41 1910 確立染色體上的基因為遺傳物質

1953 華生與克立克解出DNA的分子結構 1971 限制脢的發現, 開啟遺傳工程時代

1980第一個基因工程生物獲得專利

產業趨勢科技發展

1921 胰島素首次被鑑定出來 1928 阿司匹靈

1973 DNA複製技術 1977 發展出快速基因定序技術 1975發明出二維膠體電泳技術,開創蛋白質研究

1978第一家生技公司成立從事胰島素的量產研發

1982第一個基因重組蛋白質藥物-人類胰島素上市

1988第一個基因轉殖動物哈佛鼠獲得專利 1983 大量複製DNA之PCR技術的誕生 1990 人類基因組計劃開始

1997 Roslin Institute成功複製桃莉羊 2000 人類基因圖譜草圖

2001人類基因組計劃完

未來? 成

生物技術的科學進展

42

General mechanisms of drug action

Acting on specific proteins on cell membranes called

receptors

or intracellular receptor Block the action of specific enzymes Inhibit cell transport mechanisms Act on invading (侵入) organisms

What is “signal-transduction” ? Component ?

Signal → receptor (carrier) → transduction → response

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1. Cancer - Activating mutations or over-expression of Ras, HER2 (EGF Receptor), Akt/PKB, PI3Kinase

- Inactivation of PTEN

Most cancer genes are signal molecules or transcription factors (e.g. 50 of 100 oncogenes are kinases, the rest are kinase activators or phosphoproteins)

2. Insulin resistance - Type II Diabetes. Defects in insulin signalling means inefficient disposal of glucose

3. Alzheimer’s –  amyloid.

4. Manic depression (bipolar disorder)

- altered wnt and/or inositol trisphosphate signalling

Pain, Multiple sclerosis, hypertension, CVD, neuron injury, inflammation………

Signal transduction and disease

400 diseases coupled to kinases

44

Signal transduction vs. drug discovery

Molecular biology Cell biology

Biochemistry knowledge Physiology

Pathology pharmacology

Signal transduction

The mechanisms of development of disease

New drugs for therapy

Biomarker or therapy target

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45

Procession of the drug discovery

Signal transduction

46

Four major drug targets:

Signal transduction → development of diseases

Drug → activate/inactivate signal transduction → therapy

47

General Drug Mechanisms

Activation or prevention of activation of receptors on the surface of individual target cells.

G-protein receptors

Receptor

Ligand (Agonist - example: epinephrine)

G-protein

Ion Channel

ATP Cyclic AMP

1. Cellular Reaction

(example: in liver - glycogen to glucose) Adenyl

Cyclase

2. Movement of ions

(example: Ca⁺⁺in or out of cell) Outside

Cell

Inside Cell

Phospholipid Bi-layer

of Cell Membrane

48

Activation or prevention of activation of receptors on the surface of individual target cells (continued).

ligand regulated enzyme (tyrosine kinase) receptors

best example: Insulin receptors Ligand (the hormone Insulin)

Tyrosine Kinase activated

2. u Storage of glucose as glycogen in the liver

Glucose

1. Movement of glucose inside the cell Outside

Cell

Inside Cell

Phospholipid Bi-layer

of Cell Membrane Transport

Protein

Insulin Receptor

with Tyrosine

Kinase Glucose

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49

Activation or prevention of activation of receptors on the surface of individual target cells (continued).

ligand gated ion channel

Example: motor end plate of muscle

Acetylcholine Na⁺

K⁺

Acetylcholine binds to ion channel receptor and opens Na⁺and K⁺gates resulting in membrane depolarization

inside cell outside cell

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Interference with metabolic processes

protein synthesis regulating receptor(steroid, thyroid hormones)

Example: testosterone, thyroxine

DNA cell nucleus

transcription

translation

mRNA

protein synthesis Testosterone (or anabolic androgenic steroids)

receptor

• infertitlity

• breast development

• testicular shrinkage

• baldness

• tendon rupture

• MI’s, LVH, & Stroke

• acne & liver cysts

• cancer

• enlarged clitoris

• excess body hair

• stunted growth (STEROID SIDE EFFECTS)

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Alteration of Transport Protein Function

ion exchanger proteins

Example: Na⁺K⁺ATP-ase pump

Na⁺ K⁺

Ca⁺⁺

ATP

Ca⁺⁺extrusion is passively linked to Na⁺extrusion from repolarizing cells.

This process involves active transport and requires energy

Na⁺

Sodium - Calcium exchanger Sodium - Potassium

ATP-ase pump

52

Drug Targets

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53

Drug Targets

54

Drugs molecular target

55

以上的整理及內容告訴我們，這些和訊息傳遞有關的分子(大部份是蛋白質) ，在疾病發上扮演重要角色，也是藥物開發的分子標的

56

Signal transduction: process by which information

from the extracellular environment is conveyed into the cell interior with a change in cellular response.

from Downward, Nature, August (2001)

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Signal Transduction and Disease

G-Protein Pathway

– cholera toxin (Vibrio Cholera)

• ADP-ribosylates G_αssubunit, activates PKA--activates ion channels--excessive loss of fluid/electrolytes in intestine

Signal transduction genes are common cause of disease states

– Ras is one of the genes most commonly mutated in human tumors

• locked in the “on” (GTP) conformation

Understanding of signaling pathways has led to development of new, targetted cancer treatment

– Gleevec, a tyrosine kinase inhibitor

58

How do we link the trigger to the action?

Signal transduction

59

No cell is an island

Cell-cell interaction → function

Cells are continuously responding to signals from the

endogenous and exogenous environment ⁶⁰

The steps of Cell-Cell Communication

1. Synthesis of the signal (ligand)

2. Release of the signaling molecule by the signaling cell:

exocytosis, diffusion, cell-cell contact 3. Transport of the signal to the target cell

4. Detection of the signal by a specific receptor protein 5. A change in cellular metabolism, function or

development triggered by the receptor-signal complex 6. Removal of the signal (down-regulation)

(16)

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Origins of signal transduction research

endocrinology: chemical (hormone) signaling; receptors pharmacology: mechanisms of drug action; receptors neurosciences: neurotransmitter function; receptors

oncology: oncogenes encode signal transduction components cell biology: extracellular matrix, cytoskeletal elements

regulate cell function by signaling immunology: cytokine and interleukin biology; antigen

activation of immune cells

developmental biology: genes required for development encode signal transduction components

genomics, proteomics: 30% of metazoan genomes encode signal transduction components pharmacogenomics: signal transduction components are

drug targets

⁶²

The main principles of cell signaling:

1.Perception (感知) of the signal, usually by dedicated (專注) proteins referred to as receptors.

2.Transmission of the signal by the receptor into the cell.

3.Passing on of the “message” to a series of cell signalling components, often referred to as cell signaling cascade, as indicated by signal transduction.

4. Arrival of the message at the final destination (目的) in the cells.

5. A response by the cell, an action carried out so that the outcome is appropriate to the original signal, or stress.

Fig 1.1

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Three Steps in Cell Signaling

Target organ specificity is the result of specific receptor molecules for the hormone, either on the plasma membrane surface, or in some cases in the cytoplasm, of cells in the target organ.

1) Reception 2) Transduction 3) Response

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Cell-to-cell communication by extracellular signaling usually involves six steps

(1) synthesis of the signaling molecule by the signaling cell (2) release of the signaling molecule by the signaling cell (3) transport of the signal to the target cell

(4) detection of the signal by a specific receptor protein (5) a change in cellular metabolism, function, or development

triggered by the receptor-signal complex

(6) removal of the signal, which usually terminates the cellular

response

(17)

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Chemical signal

66

Major Forms of Cell Signaling Delivery

Hormones Adrenaline, Estradiol…

Usually carried by blood Acetylcholine

Epidermal Growth Factor NO

Delta, FasL

Signaling molecules in animals operate over various distances

67 68

(18)

69

Chemical nature of signal determines the nature of cellular interaction with receptors: polarvsnonpolarsignals

H

nonpolar

steroid hormones thyroid hormones retinoids

fatty acids

polar

neurotransmitters, peptide hormones, neuropeptides, growth factors, cytokines, interleukins ECM components, cell adhesion molecules

70

Concept of the receptor: bimodal with binding site and effector region

Nonpolar: nuclear/

cytoplasmic receptors;

transcription factors

Polar: membrane- spanning:

1. Single pass 2. 7 transmembrane 3. Multispan ion channels In all known cases, receptors are proteins or glycoproteins

71

Types of chemical signals (extracellular signals) Polar

Neurotransmitters: norepinephrine, dopamine, serotonin, acetylcholine, glutamate, GABA, glycine, adenosine

Neuropeptides: substance P, VIP, neuropeptide Y, leptin, CRF, TRH, GnRH, ghrelin, melanocortin, dynorphin, endomorphin, PACAP, bombesin, orexins, vasopressin, oxytocin, galanin, neurotensin etc

Peptide hormones: insulin, glucagon, gastrin, secretin, CCK, PTH, CGRP, calcitonin, somatostatin, LH, FSH, GH, prolactin, ACTH, angiotensin

Growth factors: TNF, TGF, EGF, VEGF, BDNF, NGF, FGF

Chemokines: interleukins 1-18, GM-CSF, G-CSF, RANTES, MIP, MCP, HCC, SDF, GRO, CCL

Developmental regulators: delta, serrate, Wnt, BMP, hedgehog, nodal Extracellular matrix: fibronectin

Adhesion molecules: cadherins

Nonpolar

Steroid hormones: estrogens, progestins, androgens, glucocorticoids, mineralocorticoids, vitamin D

Thyroid hormones Vitamin A retinoids

Fatty acids ₇₂

(19)

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Effector sites on receptors lead to transduction of signal:

initiate signaling events

Receptors for nonpolar signals: bind DNA response elements, transcription co-activators/co-repressors and organize

transcriptional activation; directly enter membrane to cytosol / to nucleus.

Usually called intracellular receptor

Receptors for polar signals: cytoplasmic domains initiate diverse events; usually called cell-surface receptor

a. ser/thr protein kinases b. tyr protein kinases

c. bind G proteins and activate enzymes or ion channels d. bind proteins

e. ion flux

G AC 74

Hydrophilic ligands bind to cell-surface receptors that can can be either integral membrane

proteins or GPI-linked

Examples:

Ion-channel-linked receptors G-protein-linked receptors Enzyme-linked receptors Non-enzyme-linked receptors

75

Hydrophobic ligands diffuse across the plasma membrane and bind to intracellular receptors in

the cytoplasm or the nucleus

Examples:

Nuclear receptors for steroid and thyroid hormones, retinoids, Vit D Some are in the cytosol and move to the nucleus after ligand binding, others are bound to DNA in the

absence of ligand ₇₆

Many hydrophobic (lipophilic) hormones are steroids, derived from cholesterol

Aldosterone:

Controls blood Na and K through effects on kidney

Cortisol: stress hormone — long-term control of blood glucose

(20)

77 78

Principal mechanism of action of steroid hormones

If receptor is cytosolic, it translocates to nucleus after steroid binds.

If receptor is nuclear, steroid enters nucleus before binding.

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Direct cell-cell signaling

Cells that are in physical contact are often very active in signaling to each other. They can achieve this by either recognition of molecules on each others’ surface or direct communication through specialized areas of the cell surface.

Ligand as a generic (通稱) term for any molecule which binds to specific sites on a protein, such as a hormone binding to its receptors

Juxtacrine

Membrane-bound signals can activate signaling following direct cell-cell interactions

Examples: Delta-Notch signaling and ephrin-Eph signaling

80

Membrane-bound signals can activate signaling following direct cell-cell interactions

Examples: Delta-Notch signaling and ephrin-Eph signaling

(21)

81

Example: contact-dependent signaling in neuronal cell fate

82 Receptor-ligand signalling

Gap junctions and plasmodesmata (in plant)

Direct cell-cell signaling

Fig 1.4b Fig 1.5

Many, but not all, plant cells also have direct cell- to cell connections but owing to the presence of a cell wall they differ from gap junctions

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Electrical vs Chemical Synapses

ELECTRICAL (gap junction)

3.5 nm pre-post distance Cytoplasmic continuity

(連續性)

Gap-junction channels Ion current

No synaptic delay Bidirectional direction of

transmission

Smooth and cardiac muscles

CHEMICAL (synapse)

20-40 nm pre-post distance No Cytoplasmic continuity

Synaptic cleft

(Ca2+ depend

neurotransmitter release) Presynaptic vesicles and

postsynaptic receptors Chemical transmitter 3 ms synaptic delay Unidirectional direction of

transmission

Functional connection between a neuron and another neuron (or effector cell such as

muscle, gland)

⁸⁴

Electrical Synapse

ELECTRICAL (gap junction)

3.5 nm pre-post distance Cytoplasmic continuity (連續性) Gap-junction channels Ion current

No synaptic delay

Bidirectional direction of transmission Smooth and cardiac muscles

(22)

85 86

87 88

(23)

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Tools for Studying Signal Transduction Recombinant proteins for in vitro studies

Antibodies to inhibit signalling function, or to measure protein levels or to localise protein or determine activation state

Modified protein expression

Specific inhibitors of enzymes or agonists/antagonists of receptors Stable membrane permeable mimetics e.g.of cyclic nucleotides Anti-sense

RNAi

Dominant negative mutants Ligand-binding site

Others:

Knockouts Modifying ion effects

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INTRODUCTION OF SIGNAL TRANSDUCTION & DRUG DISCOVERY