Neoplasia 3

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SJS- oncogene

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encodes beta chain of PDGF, which is a potent mitogen for fibroblasts, smooth muscle cells, and glial cells
astrocytomsa and osteosarcomas produce PDGF like polypeptides. tumors express receptors for PDGF

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HST 1 and INT 2

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encode homologs of FGFs; activated in GI and breast tumors. bFGF is expressed in human melanomas.

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RAS

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cause overexpression of transforming growth factor (TGF-a), which is related to EGF and is expressed in carcinomas such as astrocytomas and hepatocellular carcinoma

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HGF and its receptor c-MET

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overexpressed in follicular thyroid carcinoma

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oncogenes cause ? without binding to the growth receptor

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persistent tyrosine kinase activity

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RET

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a receptor tyrosine kinase that undergoes oncogenic conversion via mutation and gene rearrangement. it is a receptor for glial cell line-derived neurotropic facotr. pt mutation is assoc with inherited MEN 2A and 2B and familial medullary thyroid carcinoma

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point mutation of c-FMS gene

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encodes CSF-1 receptor-- has been detected in myeloid leukemia.

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ERB-B1

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EGF receptor gene (EGFR) that is overexpressed in 80% of squamous cell carcinomas of the lung and to a lesser extent in carcinomas in the bladder, GI tract, and astrocytomas.

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ERB-B2 (Her2/neu)

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amplified in 25% of breast cancers, adenocarcinomas of the ovary, lung, stomach, and salivary gland

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pt mutation in c-KIT

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encodes the receptor for stem cell factor (steel factor) associated with GI stromal tumors

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single most common abnormality of dominant oncogenes in human tumors

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mutation in RAS.
kras-- pancreatic tumors, colon, and lung
hras- bladder and kidney tumors
nras- melanomas and hematologic malignancies

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GAP

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functions as the brakes and prevents uncontrolled ras activity

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point mutation in BRAF

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detected in more than 60% of melanomas and 80% of benign nevi

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ras is also invovled in...

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cell cycle regultaion. it controls the levels of CDKs by unknown mechanisms

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c-abl

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non receptor associated tyrosine kinase that has activity that is dampened by negative regulatory domains. in CML and some ALL types, activity is unleashed bc the c-abl is translocated from normal location on chromosome 9 to the bcr region on 22. bcr-abl has tyrosine kinase activity

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following translation, c-myc...

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translocated to the nucleus, where it combines with max. the c-myc-max complex binds to E-boxes (DNA sequences) and is a potent txn activator. this activates the txn of growth related genes

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myc dysregulation

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noted in Burkitt's lymphoma (t8;14)

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N-myc amplification

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neuroblastomas

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L-myc amplifciation

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small cell carcinomas of the lung

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mutation that dysregulates activity of cyclins and cyclin-dependent kinases

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favor cell proliferation

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cyclin D genes

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overexpressed/amplified in many carcinomas, eg breast, esophagus, and liver. translocation is seen in subsets of lymphoma (mantle cells)

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amplification of CDK4 gene

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melanomas, sarcomas, and glioblastomas

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tumor suppressor genes located in the nucleus

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p53
Rb
Wt-1
p16
KLF6

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Rb

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located on chrom 13q14; germ line mutation and LOH predisposes to cancer; function is to regulate cell cycle;

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tumors assoc with somatic Rb mutation

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retinoblastoma, osteosarcoma, carcinoma of the breast, colon, and lung

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tumors assoc with inherited mutations of Rb

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retinoblastoma, osteosarcoma, and soft tissue sarcomas

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knudson "two hit" hypothesis of oncogenesis

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explains familial and sporadic occurences; in hereditary cases, one hit inherited from affected parent, and second hit in one of many retinal cells. in sporadic cases, both hits occur in retinal cells. both alleles of Rb locus must be inactivated for development of retinoblastomas

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p53 gene
guardian of the genome

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located on 17p13.1; over 50% of human tumors contain mutations in this gene; fxn is cell cycle arrest and apoptosis in response to DNA damage;

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tumors assoc with somatic mutation of p53

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most human cancers including lung, colon, and breast

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tumors assoc with inherited mutation of p53

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Li-fraumeni syndrome (multiple carcinomas- breast and brain) and sarcomas

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WT-1

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on 11p13; fxn in nuclear transcription; associated tumors: wilm's tumor (nephroblastoma)

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p16 (INK4a)

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fxn is to regulate cell cycle by inhibition of cyclin dependent kinases;

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tumors assoc with somatic mutation of p16

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pancreatic, breast, and esophageal

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tumors assoc with inherited mutation of p16:

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malignant melanoma

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KLF6

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fxn is to encode txn factor; associated in more than 70% of primary prostate cancer

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tumor suppressor genes located in the cytosol

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APC/Beta catenin
PTEN
SMAD2 and SMAD4 (DPC4)

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APC/Beta catenin

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fxn: inhibition of signal transduction; APC protein downregulates beta catenin. in absence of WNT, APC causes degredation of B cat, thus preventing its accumulation in the cytoplasm. B cat forms complex with TCF in the nucleus (txn factor)

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tumors assoc with somatic mutation of APC

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carcinomas of stomach, colon, pancreas, melanomas

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tumors assoc with inherited mut of APC

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familial adenomatous polyposis coli/colon cancer

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PTEN

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phosphatase and tensin homolog located on 10q23; activity casues cell cycle arrest by increasing txn of p27 cip/kip cell cycle inhibitors and apoptosis
tumors assoc with somatic mut: endometrial and prostate

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SMAD 2 and 4 (DPC4)

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fxn is TGF-B growth inhibitory signal transduction; SMAD4 is inactivated in 50% of pancreatic cancers; 2 is present in some colorectal cancers

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TS genes located on inner plasma membrane and cytoskeleton

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NF1
NF2

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NF1

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neurofibromin is protein prod; fxn is inhibition of RAS signal transduction and p21 cell cycle inhibotor; somatic mut: neuroblastomas; inherited mut: neurofibromatosis type 1 and sarcomas

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NF2

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merlin is protein prod; fxn is cytoskeleton stability; somatic mut: schwannomas and meningiomas; inherited mut: NF type 2, acoustic schwannomas and meningiomas

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TS genes located on cell surface

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TGF-B receptor
E-cadherin

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TGF-B receptor

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fxn in growth inhibition
tumors assoc with somatic mut: carcinoma of colon

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E-cadherin

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fxn in cell adhesion; somatic mut: carcinoma of stomach; inherited: familial gastric cancer

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evasion of apoptosis

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BCL-2

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BCL-2

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85% of follicular B cell lymphomas carry a characteristic t(14;18)(q32;q21) translocation which prevents apoptosis. pro apoptotic members of family are Bak, Bax, and Bim

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Defects in DNA repair system

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mismatch repair
nucleutide excision repair
diseases with defect in DNA repair by homologous recombination

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mismatch repair (spell checkers)

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microsatellite instability is hallmark; (hereditary nonpolyposis cancer syndrome)- cancers of cecum and proximal colon (pts <50yrs); also assoc with endometrial and ovarian cancers; germ line mutation of MSH2 (2p16) and MLH1(3p21) account for 30% of cases

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NER

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XP--pt at increased risk of skin cancer when exposed to UV rays. UV light causes cross linknig of pyrimidine residues

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diseases with defect in DNA repair by homologous recombination

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AR disorders: ataxia-telangectasia, Bloom syndrome, and Fanconi anemia

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BRCA-1 and BRCA-2 Genes

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Individuals who inherit mutations of BRCA 1 and 2 susceptible to breast cancer.
Germ line mutation of BRCA-1: breast and ovarian cancer
Germ line mutation of BRCA-2: ovary (<BRCA-1) and male breast cancer.
10-20% of breast cancers are familial and mutation of BRCA-1 and BRCA-2 account for 80% of familial breast cancer.
The mutation is present in < 3% of all breast cancers.