Viral Oncogenesis – Oncogenes and Proto-Oncogenes

Flashcards of key vocabulary terms and definitions from the lecture notes on Viral Oncogenesis, Oncogenes, and Proto-Oncogenes.

Oncogenes

Contribute to tumor development through increased or misdirected activity, stimulating cellular proliferation, inhibiting differentiation, and suppressing apoptotic pathways.

Tumor Suppressor Genes

Counteract oncogenic processes by inhibiting proliferation, promoting cellular differentiation, and stimulating apoptosis in cells with DNA damage.

Proto-oncogenes

Normal cellular genes that regulate essential functions in cell growth and survival, maintaining controlled cellular proliferation and differentiation.

RAS

A proto-oncogene involved in signal transduction.

MYC

A proto-oncogene that regulates gene transcription.

EGFR

Epidermal growth factor receptor mediating growth signals; a proto-oncogene.

SRC

A non-receptor tyrosine kinase controlling multiple cellular processes; a proto-oncogene.

Point Mutations (Proto-Oncogene Conversion)

Alter protein structure, causing continuous activation of growth signaling pathways, e.g., KRAS in pancreatic and colorectal cancers.

Gene Amplification (Proto-Oncogene Conversion)

Increased copy number of proto-oncogenes leading to protein overexpression, e.g., HER2 in breast cancer.

Chromosomal Translocation (Proto-Oncogene Conversion)

Rearrangement of chromosomal segments creating fusion genes with aberrant function, e.g., BCR-ABL fusion in chronic myeloid leukemia.

Viral Insertion (Proto-Oncogene Conversion)

Integration of viral DNA near proto-oncogenes or introduction of viral oncogenes disrupting normal regulation, e.g., HTLV-1 Tax protein activating cellular transcription factors.

Growth Factors (Oncogenes)

Proteins like Platelet-Derived Growth Factor (PDGF) that stimulate cell proliferation by binding to specific receptors.

Growth Factor Receptors (Oncogenes)

Transmembrane proteins including ROS and TRK that transduce external growth signals into intracellular responses.

Signal Transducers (Oncogenes)

GTP-binding proteins and non-receptor protein kinases that relay signals from receptors to downstream effectors.

Transcription Factors (Oncogenes)

Nuclear proteins that control gene expression programs regulating proliferation, differentiation, and apoptosis.

Apoptosis Regulators (Oncogenes)

Proteins that control programmed cell death; oncogenic versions typically suppress apoptotic pathways.

MYC Oncogene

A transcription factor that regulates approximately 15% of all genes, playing critical roles in cell cycle progression, cellular differentiation, programmed cell death, and blood vessel formation.

RAS Oncogene

Small GTPases that function as molecular switches in signal transduction pathways, controlling fundamental cellular processes including cytoskeletal integrity, proliferation, differentiation, adhesion, apoptosis, and migration.

p53

A tumor suppressor protein that oversees critical cellular processes including DNA repair, apoptosis, and cell cycle regulation, preventing neoplastic transformation.

Viral Oncogenesis

The complex molecular and cellular processes through which viruses contribute to cancer development, involving viral integration into host genomes, expression of viral oncoproteins, and disruption of normal cellular regulatory pathways.

Tumor Suppressor Inactivation (Viral Oncogenesis)

Viral proteins bind to and inactivate crucial tumor suppressor genes like p53, removing critical checkpoints against abnormal cell proliferation.

Insertional Mutagenesis (Viral Oncogenesis)

Viral genomes integrate into host DNA, potentially disrupting tumor suppressors or activating proto-oncogenes.

Viral Oncogenes

Viruses encode proteins that directly promote cellular proliferation and survival, often mimicking growth factors or their receptors.

Human Papillomavirus (HPV)

A DNA oncogenic virus; high-risk types 16 and 18 cause cervical cancer through E6/E7 oncoproteins.

Epstein-Barr Virus (EBV)

A DNA oncogenic virus associated with Burkitt's lymphoma, Hodgkin lymphoma, and nasopharyngeal carcinoma.

Hepatitis B Virus (HBV)

A DNA oncogenic virus that contributes to hepatocellular carcinoma through chronic inflammation and the HBx protein.

Kaposi's Sarcoma-associated Herpesvirus (KSHV)

A DNA oncogenic virus that causes Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease.

Human T-cell Leukemia Virus Type 1 (HTLV-1)

An RNA oncogenic virus that causes adult T-cell leukemia/lymphoma through the Tax oncoprotein.

Hepatitis C Virus (HCV)

An RNA oncogenic virus associated with hepatocellular carcinoma, primarily through chronic inflammation mechanisms.

Rous Sarcoma Virus (RSV)

A retrovirus that transforms normal fibroblasts into cancerous cells through constitutive tyrosine kinase activity of the Src protein.