DF/HCC Program Affiliation

Breast Cancer

Research Abstract

Our long term interest is to elucidate the molecular events involved in the genesis of breast cancer. Substantial evidence exists supporting direct roles for ErbB-2/neu and Src tyrosine kinase activation in breast cancer. CHK (Csk Homologous Kinase) is a cytoplasmic protein tyrosine kinase that phosphorylates and negatively regulates Src kinase activity. CHK is highly restricted in its expression and normally found in brain and hematopoietic cells. Our recent studies reveal that CHK expression was observed in 70 out of 80 primary breast cancer specimens, but not in normal breast tissues (0/19). Confocal microscopy analysis revealed co-localization of CHK with ErbB-2 and Src in these primary specimens (6/6). Furthermore, we observed that CHK participates in signaling in breast cancer cells by associating, via its SH2 domain, with ErbB-2 following heregulin stimulation. This association appears to be receptor specific (ErbB-2) and ligand specific (heregulin). Site-directed mutagenesis and phosphopeptide inhibition experiments indicated that CHK-SH2 binds to Tyr1253 of the rodent ErbB-2 (neu) or to Tyr1248 of the human ErbB-2. Moreover, CHK was able to downregulate ErbB-2/neu-activated Src kinases. Overexpression of CHK in MCF-7 breast cancer cells markedly inhibited cell growth and proliferative response to heregulin as well as decreased colony formation in soft agar. We aim to further assess the expression of CHK, relative to Src and ErbB-2 tyrosine kinases, in human breast tumors resected at various stages of malignant progression, and to determine the molecular and functional analyses of CHK-ErbB-2 and CHK pp60Src interactions in breast cancer cells. In addition, we aim to characterize the biological role(s) of CHK in breast cancer cellular responses and cell growth and to identify and characterize signaling molecules that associate with CHK in breast cancer cells.

Another interest involved functional characterization of a novel BRCA2-locus gene, AER, in breast cancer. Recent observations in our laboratory have indicated that the cytoplasmic tyrosine kinase RAFTK, which was originally cloned in our laboratory, interacts with a novel protein, as demonstrated by the yeast two-hybrid system and confirmed by a biochemical approach. We have termed this novel protein AER. This protein bears homology to the product of BRCA2's transcription unit, CG003. The overall goal is to investigate the function(s) of the AER protein in breast cancer cells.

A recent interest in our group is to elucidate the biological function of BRCA1. Our recent studies showed that heregulin stimulation induced the phosphorylation of BRCA1 activation and the serine/threonine kinase, AKT, in T47D human breast cancer cells. The heregulin-induced phosphorylation of BRCA1 was abrogated by PI3-K inhibitors and by a dominant-negative AKT. Furthermore, in the absence of heregulin, the ectopic expression of the constitutively active p110 subunit of PI3-K was sufficient to induce BRCA1 phosphorylation. This is a novel signaling pathway by which heregulin regulates BRCA1, and that BRCA1 phosphorylation is mediated by the PI3-K/AKT pathway upon heregulin stimulation of breast cancer cells. We aim to examine BRCA1 function and regulation in breast cancer. Since our observations indicate that BRCA1 phosphorylation is mediated by PI3-K/AKT and since PTEN and ECM were reported to regulate PI3-K/AKT signaling, we aim to characterize the biological function of BRCA1 and the role of PTEN and ECM in regulating BRCA1 activation and function.

Publications

• Jiang S, Seng S, Avraham HK, Fu Y, Avraham S.Process Elongation of Oligodendrocytes Is Promoted by the Kelch-related Protein MRP2/KLHL1.J Biol Chem 2007 Apr 20;282(16):12319-29.
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• Lee TH, Seng S, Li H, Kennel SJ, Avraham HK, Avraham S.Integrin regulation by vascular endothelial growth factor in human brain microvascular endothelial cells: role of alpha6beta1 integrin in angiogenesis.J Biol Chem 2006 Dec 29;281(52):40450-60.
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• Seng S, Avraham HK, Jiang S, Venkatesh S, Avraham S.KLHL1/MRP2 mediates neurite outgrowth in a glycogen synthase kinase 3beta-dependent manner.Mol Cell Biol 2006 Nov;26(22):8371-84.
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• Kaminski R, Zagozdzon R, Fu Y, Mroz P, Fu W, Seng S, Avraham S, Avraham HK.Role of SRC kinases in Neu-induced tumorigenesis: challenging the paradigm using Csk homologous kinase transgenic mice.Cancer Res 2006 Jun 1;66(11):5757-62.
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• Park I, Avraham HK.Cell cycle-dependent DNA damage signaling induced by ICRF-193 involves ATM, ATR, CHK2, and BRCA1.Exp Cell Res 2006 Jul 1;312(11):1996-2008.
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• Lee BC, Lee TH, Zagozdzon R, Avraham S, Usheva A, Avraham HK.Carboxyl-terminal Src kinase homologous kinase negatively regulates the chemokine receptor CXCR4 through YY1 and impairs CXCR4/CXCL12 (SDF-1alpha)-mediated breast cancer cell migration.Cancer Re
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• Bu X, Avraham HK, Li X, Lim B, Jiang S, Fu Y, Pestell RG, Avraham S.Mayven induces c-Jun expression and cyclin D1 activation in breast cancer cells.Oncogene 2005 Mar 31;24(14):2398-409.
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• Avraham HK, Lee TH, Koh Y, Kim TA, Jiang S, Sussman M, Samarel AM, Avraham S.Vascular endothelial growth factor regulates focal adhesion assembly in human brain microvascular endothelial cells through activation of the focal adhesion kinase and related ad
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• Miralem T, Avraham HK.Extracellular matrix enhances heregulin-dependent BRCA1 phosphorylation and suppresses BRCA1 expression through its C terminus.Mol Cell Biol 2003 Jan;23(2):579-93.
  12509456
• Lee TH, Avraham HK, Jiang S, Avraham S.Vascular endothelial growth factor modulates the transendothelial migration of MDA-MB-231 breast cancer cells through regulation of brain microvascular endothelial cell permeability.J Biol Chem 2003 Feb 14;278(7):527
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• Kim S, Zagozdzon R, Meisler A, Baleja JD, Fu Y, Avraham S, Avraham H.Csk homologous kinase (CHK) and ErbB-2 interactions are directly coupled with CHK negative growth regulatory function in breast cancer.J Biol Chem 2002 Sep 27;277(39):36465-70.
  12122014
• Li H, Lee TH, Avraham H.A novel tricomplex of BRCA1, Nmi, and c-Myc inhibits c-Myc-induced human telomerase reverse transcriptase gene (hTERT) promoter activity in breast cancer.J Biol Chem 2002 Jun 7;277(23):20965-73.
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