Elevated content of the tyrosine kinase substrate phospholipase C-gamma 1 in primary human breast carcinomas.

Abstract

Phospholipase C-yl (PLC-yl) is a substrate for several receptor tyrosine kinases and its catalytic activity is increased by tyrosine phosphorylation. However, the biological significance of this molecule in normal or malignant human epithelial cell proliferation is unknown. We determined the relative content of PLC-yl in primary human mammary carcinomas and in nonmalignant mammary tissues. By Western blot and immunohistochemistry, considerably higher levels of PLC-yl protein were detectable in the majority of carcinomas and in one of two benign fibroadenomas compared to normal breast tissues. In 18 of 21 carcinomas that contained high levels of PLC-y1, the presence of phosphotyrosine on PLC-yl could also be detected. All carcinomas in which tyrosine phosphorylated PLC-y1 was present also expressed detectable levels of the epidermal growth factor receptor or erbB-2, two tyrosine kinases known to phosphorylate this enzyme. Thus, a high percentage of mammary carcinomas concomitantly display increased levels of receptor tyrosine kinases and a direct tyrosine phosphorylation substrate, thereby potentially amplifying two successive steps in a signal transduction pathway.Recently, several reports have demonstrated that phospholipase C-yl (PLC-yl) is a direct substrate of the epidermal growth factor (EGF) receptor protein tyrosine kinase (1-4). PLC isoenzymes hydrolyze phosphatidylinositol 4,5-bisphosphate to produce two intracellular second messengers: inositol 1,4,5-trisphosphate and 1,2-diacylglycerol (5), which regulate intracellular levels of Ca2l and protein kinase C activity, respectively. As much as 50-70% of the total cellular pool of PLC-yl becomes tyrosine phosphorylated within 1 min after the addition of EGF to cells (2,3,6). Importantly, growth factor-induced tyrosine phosphorylation increases the catalytic activity of 8). In vitro experiments show that the purified EGF receptor phosphorylates PLC-yl but does not significantly phosphorylate the PLC-p and 8 isoenzymes (4). However, not all tyrosine kinases phosphorylate PLC-yl. Although the plateletderived growth factor (PDGF) (3, 9), fibroblast growth factor (10), nerve growth factor (11), and erbB-2 receptors (12, 13) also phosphorylate PLC-yl, insulin and colony-stimulating factor type 1 receptors do not utilize PLC-'yl as a substrate (3,14,15). Taken together these data suggest that phosphorylation of PLC-yl is a biologically important event in growth factor-stimulated inositol phospholipid metabolism and perhaps plays a role in signal transduction for cell proliferation. However, most of these studies have utilized cultured A-431 human squamous carcinoma cells or mouse 3T3 fibroblasts transfected with wild-type human EGF receptors. Studies in human tissues are lacking and, although PLC-yl is ubiquitously distributed in animal tissues, factors that may influence its level of expression are unknown.To provide evidence for a functional role of PLC-'yl in proliferating human epithelial tissues, we have examined PLC-yl levels in benign and malignant ...

Combinatorial synergy induced by adenoviral-mediated mda-7 and Herceptin in Her-2+ breast cancer cells

“…GSK3b, a member of the Wnt signaling pathway, plays a key role in various cellular processes including cell proliferation and embryonic development, via regulation of apoptosis and b-catenin. 39 Our studies show that Admda7, alone and in combination with Herceptin, is able to downregulate PLC-g and upregulate GSK-3b (data not shown). GSK-3b phosphorylates b-catenin and activates its ubiquitin-mediated degradation, inhibiting its translocation to the nucleus, thereby preventing cancer cell proliferation and invasiveness.…”

The mechanism of phospholipase C-γ1 regulation

“…The expression level of PLC-γ1 is increased in human colorectal cancer, human breast carcinomas, familial adenomatous polyposis, and human skins under hyperproliferative conditions (Arteaga et al, 1991;Nanney et al, 1992;Park et al, 1994;Noh et al, 1994). In addition, the transcriptional activity of PLC-γ1 is up-regulated in cancer tissues.…”

The protein-tyrosine phosphatase DEP-1 modulates growth factor-stimulated cell migration and cell–matrix adhesion

“…Anti-v-src (Ab1, clone 327) antibody agarose-linked for immunoprecipitation, was from Calbiochem-Novabiochem (Bad Soden, Germany). Anti-hPDGFb-receptor monoclonal antibodies (Ro¨nnstrand et al, 1988) and anti-PLCg1 antibodies (Arteaga et al, 1991) were described earlier. Anti-p85 antibodies were from Upstate Biochemicals (Lake Placid, NY, USA).…”