Self- Sufficiency in growth signals Cancer.

1. Self-Sufficiency in Growth Signals TSMU Siddhant Kushare Group 1 Semester 5

2. What is Proto-Oncogene and Oncogene • Proto-oncogenes are normal cellular gene which causes cell growth and proliferation, After required growth is achieved, proto-oncogenes are switched off and then we can say that Normal Activity of proto-oncogenes are regulated (Controlled). • Oncogenes are mutated version of Proto-Oncogene or Overexpressed version, They are encoded and promotes excessive growth and proliferation in absence of any growth promoting signals. Activity of oncogenes cannot be regulated ( Not Controlled).

3. How Does Normal Cell Responds To Growth Factor. • Aberration can occur at any point: • Growth Factor • Growth Factor Receptor • Protein Involved In Signal Transduction • Nuclear Regulatory Protein (Transcription Factor) • Proteins Involved In Cell Cycle Regulation( Cyclins , Cyclin Dependent Kinase)

4. Growth Factor • A growth factor is a naturally occurring substance capable of stimulating cell proliferation, wound healing and occasionally cellular differentiation. • Usually it is secreted Protein or a steroid hormone. • Most soluble growth factor are made by one cell type and act on neighbouring cell to stimulate proliferation (paracrine action)

6. Growth Factor Receptor • From Large No. of Oncogenes encoded Growth Factor Receptor, Receptor Tyrosine Kinase (RTK) are most important. • There is auto phosphorylation of tyrosine residues in its own tail -> RAS • But in Cancer , These GFR[R.T.K] are mutated, leading to constitutive GF independent Tyrosine Kinase activity. • RTK are constitutively activated in tumor a by multiple mechanisms including Pt.mutations, Gene Re-arrangements and Gene amplification.

8. Proteins Involved In Signal Transduction • Cancer cells often acquire growth autonomy as a result of mutations in genes that encode components of signaling pathways downstream of growth factor receptors. • There are 2 important oncoprotiens in category of signaling molecules are RAS and ABL . • RAS is most commonly mutated and Important signal transduction protein.

9. RAS Protein • RAS is a member of a family of small G proteins that bind GTP and GDP. • Activated RAS stimulates downstream regulators of proliferation by several interconnected pathways that converge on the nucleus and alter the expression of gene that regulate growth, such as MYC. • RAS most commonly is activated by point mutations in amino acid residues that are either within the GTP-binding pocket or in enzymatic region that carries out GTP hydrolysis. • Gain of function mutation in RAS cause uncontrollable activity And Loss of function mutations in GAP also cause uncontrollable RAS activity.

10. Mutation in MAP-K and P13K/AKT Cascade • Both MAP-K and P13K/AKT lie downstream to RAS. • Mutation in BRAF It is a member of RAF Family Serine / Threonine protein kinases. Present in 100% hairy cell leukaemia >60 %Melanomas Langerhan cell histiocytosis Colon Cancer BRAF Activation mutation will stimulate MAP-K pathway which will increase downstream growth pathway.

11. Mutation in kinases of P13K family Very common in certain Cancers RTK —>ATK (major signaling node) —>mTOR —>Protein and lipid synthesis . P13K is regulated by a breaking Factor called PTEN which converts P13K to ATK ( due to which there is decrease signal transduction) Gain of function mutation in P13K causes 30% breast Cancer. PTEN —> Tumor suppressor gene ( decreases signaling transduction). Loss of function mutation causes Cancer. • Oncogene Addiction: Phenomenon where some tumors are dependent on single oncogenic protein for sustained Growth and proliferation. Inhibition of this specific oncogene is sufficient to halt the neoplastic phenotype.

12. Non-Receptor Tyrosine Kinase • They can have 2 forms of mutations • Mutation in form of chromosomes translocation or re-arrangements: - They create Fusion genes -encode constitutively active tyrosine kinase. In chronic myelogenous leukaemia (CML) and some ALL,ABL gene is translocated from its normal location on chromosome 9 to chromosome 22 where it fuse at the BCR gene to form ABL-BCR hybrid gene which activates growth signalling pathways.

13. BCR-ABL Hybrid Gene are Chimeric Gene. • BCR-Moiety promotes self association of BCR-ABL which is sufficient to unlease the tyrosine kinase activity of ABL. • Treatment for CML is to give BCR-ABL kinase inhibitors. • Rare CML stem cells persist, which harbour BCR-ABL Fusion gene, apparently because these cells do not require BCR-ABL signals for their survival. That’s why treatment is life long . • N.R.T.K are also affected by point mutations: N.R.T.K normally have negative auto-regulatory function that keeps enzyme activity in check. One ex. JAK-2 so point mutation in JAK-2 due to which there will be constitutive JAK/STAT signalling pathway. Due to which tumor is relieved from normal dependence on growth factor.

15. Nuclear Regulatory Protein • All signal transduction pathways converge onto the nucleus. • This proteins stimulate the transcription factors and Enter cell cycle resulting in growth and proliferation. • Normally there is a transient activation of transcription factors but mutations in transcription factor will lead to uncontrolled cell cycle causing growth and proliferation. • Transcription Factors includes: MYC,MYB , JUN , FOS , REL

16. The most common TF encoded protooncogene tonne mutated in cancer is MYC. • MYC- Oncogene : Normally they are rapidly and transiently induced by RAS / MAP-K signalling. MYC activate expression of many genes that are involved in cell growth: • MYC targets genes like D-Cyclins which are directly involved in cell cycle progression. • MYC unregulates expression of rRNA and increase rRNA processing resulting in increased protein synthesis. • MYC is also involved in Metabolic Reprogramming(Warburg- effect)which is one of the hallmark of cancer . MYC will stimulate multiple glycolytic enzymes and Factors involved in Gultaming Metabolism which leads to synthesis of macromolecules like DNA, Protiens and Lipids which are the requirements of cancer cells.

17. MYC is the master transcription regulator for cell growth ex. Burkett lymphoma . • MYC increases expression of telomerase. • MYC is capable of converting somatic cells to stem cells —> cancer cells. • Mutations involving MYC are: • Translocations which involves MYC oncogene which places MYC under control of enhancer’s causing increased MYC expression. Examples are Burkett lymphoma and few B&T cell tumors. • Amplification of MYC oncogene such as in Breast , colon , lung cancers. Some other examples are N-MYC( neuroblastoma) and L-MYC ( small cell carcinoma of the lung) • Increased upstream signaling pathway: such as RAS/MAP-K signaling pathways, Notch signaling, WNT signaling, Hedge Hog signaling pathway this all pathways are up regulator of MYC

18. Cyclins and Cyclin-Dependent Kinases • Growth factors transduce signals that stimulate the orderly progression of cells through the various phases of cell cycle, the process by which cells replicate their DNA in preparation for cell division. This cell cycle is orchestrated by Cyclin-dependent kinases which are activated by binding to Cyclins. • CDK-cyclin complex phosphorylate crucial target protiens that drive cells forward through the cell cycle. CDK inhibitors silence CDKs and exert negative control over the cell cycle, Expression of these inhibitors is down regulated by mitogenic signaling pathway causing progression of cell cycle.

19. Cell Cycle Checkpoints : G1/S : Checks the DNA integrity before allowing DNA replication. G2/M : Ensures there has been accurate DNA replication by the cell actually divides. • Cell cycle is regulated by activators and inhibitors: • Cyclins : they are protiens synthesised sequentially during cell cycle(D-E-A-B) , they activate CDK by oxidative phosphorylation. They bind to form Cyclin-dependent complex. • CDK : this are constitutively inactive and are activated by relevant cyclins . Ex. CDK 4,6,2,1. CDK-4/ Cyclin D , CDK-6/Cyclin D , CDK-2/Cyclin E/A , CDK-1/Cyclin A/B.

20. Inhibitors: Cyclin Dependent Kinase Inhibitors (CDK-I) enforcers cell cycle checkpoints by inhibiting cyclin-CDK complex . There are total 2 families