1

Molecular mechanism of cancer metastasis

Dr. Yick-Pang Ching Department of PathologyRoom L7-05, Faculty Medicine BuildingTel: 28199656E.Mail: ypching@hkucc.hku.h

2

Overview

What is metastasis?

Molecular mechanisms of metastasis

Signalling pathways involved in metastasis

3

I) What is cancer metastasis?

Cancer defines as a population of cells that have lost their normal controls of growth and differentiation and are proliferating without check.

Metastasis is the process by which a tumor

cell leaves the primary tumor, travels to a distant site via the circulatory system, and establishes a secondary tumor.

4

Forms of cancer metastasis

5

Preferential metastatic sites

Primary tumour Common distant site (s)Breast’ adenocarcinoma Bone, brain, adrenal

Prostate adenocarcinoma Bone

Lung small cell carcinoma Bone, brain, liver

Skin cutaneous melanoma Brain, liver, Bowel

Thyroid adenocarcinoma Bone

Kidney clear cell carcinoma Bone, liver, thyroid

Testis carcinoma Liver

Bladder carcinoma Brain

Neuroblastoma Liver, adrenal

6

Reason for organ selectivity

Mechanistic theory: determined by the pattern of blood flow.

“Seed and soil” theory: the provision of a fertile environment in which compatible tumor cells could grow

7

Determining factors

Appropriate growth factors or extracellular matrix environment

Compatible adhesion sites on the endothelial lumenal surface

Selective chemotaxis at which the organ producing some soluble attraction factors to the tumor cells

8

II) Molecular mechanisms of metastasis

9

5 major steps in metastasis

1. Invasion and infiltration of surrounding normal host tissue with penetration of small lymphatic or vascular channels;

2. Release of neoplastic cells, either or single cells or small clumps, into the circulation;

3. Survival in the circulation; 4. Arrest in the capillary beds of distant organs;5. Penetration of the lymphatic or blood vessel

walls followed by growth of the disseminated tumor cells

10

11

Stages of metastasis

Invasion : primary tumour cells enter circulation

Circulation to the secondary site of tumour growth

Colonisation : formation of secondary tumour

12

Tumor invasion

1. Translocation of cells across extracellular matrix barriers

2. Lysis of matrix protein by specific proteinases

3. Cell migration

13

Components of invasion

a) Matrix degrading enzymes

b) Cell adhesion

c) Cell motility

14

a) Matrix degrading enzymes

Required for a controlled degradation of components of the extracellular matrix (ECM)

The proteases involved in this process are classified into serine-, cysteine-, aspartyl-, and metalloproteinase.

15

MMP family

16

Matrix metalloproteinases (MMP)

16 members, subdivided into 4 groups, based on their structural characteristics and substrate specificities

Soluble and secreted groups; collagenase, gelatinase and stromelysins

Membrane type (MT-MMP) group are anchored in the plasma membrane

A zinc ion in the active centre of the protease is required for their catalytic activities.

17

Regulation of MMP

MMP is controlled by an increased expression on a transcriptional level.

MMPs are calcium-dependent proteases, which are synthesized as a inactive proenzymes and are activated by the cleavage of a propeptide.

MMP activity is regulated by specific inhibitors, the tissue inhibitors of MMP (TIMPs). Binding TIMP to MMP is in a 1:1 stoichiometry.

MMP2 and MMP9, which cleave type IV collagen the major constituent of basement membrane, are believed to be of special importance

18

Serine proteases

Serine protease involved in ECM degradation are plasmin, plasminogen activators and cathepsin G.

Plasmin is believed to be the most important serine protease, firstly because its ability to degrade several matrix components like gelatin, fibronectin or laminin, and secondly by the possible activation of numerous proforms of MMPs by propeptide cleavage.

Plasmin is synthesized in its inactive proform, plasminogen, which can be converted to plasmin by plasminogen activator.

19

Plasminogen activator

Two main types : urokinase (uPA) and tissue (tPA).

uPA is bound to the surface of tumor cells by means of a specific receptor (uPAR)

There are specific inhibitors (PAI-1 and PAI-2) for the PA.

20

Interaction between tumour cells and the surrounding connective tissue

21

Cell adhesion and metastasis

22

b) Cell attachment

1. Integrin: cell-matrix adhesion

2. E-cadherin/catenin adhesion complex: cell-cell adhesion

23

1) Integrin

Heterodimeric transmembrane receptors consists of and subunits

Function to provide interactions between cells and macromolecules in the ECM

Integrin can affect the transcription of MMP genes

24

Integrin signaling

25

2) E-cadherin and catenin complex

Most important cell-cell adhesion molecules

Reduce expression of E-cadherin and catenin increase the invasiveness of tumor cells

26

Cadherin-mediated cell-cell adhesion

27

p120 catenin

28

29

c) Cell migration

1. Small Rho GTPase family

2. Motility promoting factors

30

Small Rho GTPase Stimuli

Cdc42GTP

Rac1GTP

Pak1

LIM kinase

Cofilin

Actin polymerisation

MLC Kinase

MLC Phosphorylation

Contraction

Stress fibers

Detachment

Filopodia Lamellipodia

31

Model of Rho GTPase regulation

32

Regulation of Rho GTPase

33

Cell movement

34

Rho GTPase is required for the transition of invasive phenotype

35

Signaling pathways related to integrin and small GTPase

36

E-cadherin and Rho GTPase signaling

37

Rho GTPase at different stages of tumour progression

38

2) Motility promoting factors

Hepatocyte growth factor/scattering factor

Insulin-like growth factor II

Autotaxin

39

HGF/scatting factor

Heterodimer of and chains

HGF normally acts as a paracrine growth factor, but in tumor cells it can act as an autocrine

HGF binds to the c-Met receptor and activated the downstream effectors

40

HGF induce cell scattering and invasion

41

HGF induce the formation of branched tubules

42

Signalling pathways responsible for MET-dependent invasive growth

43

HGF/Met regulate integrin, cadherin and MMPs during invasion