VIII Curso Internacional del PIRRECV Some molecular mechanisms of cancer Laboratorio de Comunicaciones Celulares, Centro FONDAP Estudios Moleculares de la Celula (CEMC), ICBM, Facultad de Medicina, Universidad de Chile A.F.G. Quest, aquest@med.uchile.cl
Deaths in Chile, 1970, 1990, 2004
Prevalence of different types of cancer in Chile Organ/ranking female male 1 st 2 nd 3 rd 6th 7th 11th 10th
MODEL OF COLON CANCER Normal Tissue Polyps & Adenomas Adenocarcinoma
Normal Colon Colorectal Cancer Cell Death Proliferatión Apoptosis Apoptosis Proliferation Apoptosis Proliferation Normal Cancer Normal
COLON CANCER Polyps & Adenomas Infiltration of ganglia Adenocarcinoma Metastasis E-cadherin
What happens when cancer develops? Molecular changes In cancer, cellular communication is altered. For example: 1. Loss of contact inhibition 2. Increased sensitivity to growth factors 3. Reduced cell death
Acquired capabilities of cancer cells
Some signalling elements relevant to cancer
Parallel pathways of tumorigenesis
Some signalling elements relevant to cancer
Oncogenes & Tumor suppressors
What are oncogenes? The genetic mechanisms of transformation were discovered through the actions of transforming viruses, in which the transforming effect could be mapped to specific oncogenes. DNA viruses express proteins analogous to key proliferation factors; e.g. adenovirus E1A or SV40 large T The oncogenes of RNA retroviruses are not merely substitutes, but are derived from critical cellular regulatory genes with gain of function mutations (c-src or v-src) Evidence suggests that cancer actually develops from within, rather than via infection, by accrual of genetic changes affecting cell regulation Examples: Oncogene proto-oncogene function virus induced tumor abl protein tyrosine kinase mouse leukemia bcl-2 anti-apoptotic factor lymphoma erb-b EGF-receptor/tyrosine kinase chicken fibrosarcoma fos nuclear transcription factor mouse osteosarcoma jun AP-1 transcription factor chicken fibrosarcoma mos ser-thr kinase mouse sarcoma myc nuclear protein chicken myelocytoma H-ras GTP protein rat sarcoma sis platelet derived growth factor monkey sarcoma src non-receptor tyrosine kinase chicken sarcoma
Src Tyrosine Kinases Structural Features Membrane Attachment c-src Unique SH3 SH2 L Catalytic Negative Regulatory G2,C3,C5(6) K Y Y Membrane Attachment v-src Unique SH3 SH2 L Catalytic * **** * *** * G2,C3,C5(6) K Y (*) amino acid substitutions Modified from NRM&CB 2:467, 2001
The Ph Chromosome: t(9;22) Translocation Abl = Abelson tyrosine kinase Bcr = breakpoint cluster region
Inactive Structure of Abl cap N-lobe C-lobe
What are tumor suppressors? Some genes appear to be oncogenic upon loss of function, and therefore act as proliferation regulators or tumor suppressors. These include prb105 or p53, originally misclassified as oncogenes, or the more recently discovered BRCA1. Others include APC (adenomatous polyposis coli protein) These are classic examples of tumor suppressor molecules that were discovered as mutations associated with disease states. Such mutations can be either of germline (hereditary)or somatic origin. More recently, tumor suppressors are characterized based on functional properties and association of changes in expression patterns with certain disease states. An example here is Caveolin-1.
Cell proliferation
Receptor Tyrosine Kinases
Signaling cascade downstream of RTKs
Unlimited replicative potential
Telomers and telomerases The Hayflick limit, of some 50-70 division cycles for human diploid fibroblasts, is mediated by telomere length. Telomerase is active in germline cells, but inactive in somatic cells. Cells reach senescence when the short telomeres trigger the protective mechanisms of p53, which stimulates the CKIs to halt further cell cycle progress. Cells reach crisis when telomeres are lost, exposing chromosome ends, and provoking the double strand repair mechanism to make inappropriate attempts at recombination and ligation. In some cases, immortalized cells maintain telomeres by reactivating telomerase, and maintain relatively stable chromosomes. However, a significant proportion of immortalized cells are viable in the absence of telomerase, and use a less well characterized process alternative of telomeres (ALT).
Cell survival & cell death
The major PI3-kinase signalling pathways and functions Mol.Med. Today (2000) 6: 338
Kang et al., PNAS102-802
Two major apoptotic pathways in mammalian cells
Appearance of Phosphatidylserine on the Surface of Apoptotic Cells
Ingestion of apoptotic bodies by a macrophage
Angiogenesis
Angiogenesis
O 2 -dependent modulation of HIF activity
Receptor Tyrosine Kinases: VEGF The VEGF receptor is a receptor tyrosine kinase of the PDGF type!
Cell adhesion
The Integrin-Extracellular Matrix (ECM) signalling system The integrin family consists of α,β heterodimers (about 18α and 8β subunits) Transmembrane proteins with short intracellular domains. Integrate interactions between cytoplasm and ECM. Binding proteins of the ECM contain contain target RGD or related sequence (collagens, laminins, fibronectin) Also known now to interact with cell surface proteins (Thy-1)
Cell adhesion and survival
Cell-cell contact
Cell-cell signalling and contact inhibition: cadherins Cell-cell interactions and signalling involve proteins called cadherins (Ca dependent adhesion proteins) and intracellular effectors called catenins. Different cadherins are associated with different cell types, e.g. N-cadherin (neural), M-cadherin (mesenchyme), E-cadherin, (epithelial). Cadherins mediate self recognition by binding another identical cadherin as their extracellular ligand. Loss of E-cadherin promotes Epithelial-Mesechymal Transition (EMT)
Caveolin-1 as a tumor suppressor: Working model Quest lab
Metastasis
Metastasis
Loss of cellular adhesion Metastasis Increased invasive capacity Onset of metastasis is associated with changes in the expression of cell surface molecules: - loss of E-cadherin, which is important for cell-cell interaction - change in the expression pattern of integrins (αxβy), which are important for cell-matrix interactions - increase/change in the expression of matrix metalloproteinases (MMP9)
Hallmarks of tumorigenicity and cancer Disregard of signals to stop proliferating and to differentiate Autonomous generation of signals that promote growth Capacity for sustained proliferation Evasion of apoptosis Motility and invasiveness Angiogenesis.
Emerging and Enabling Hallmarks
Tumors as complex tissues