Autocrine/Paracrine Regulation of Breast Cancer Cell Proliferation by Growth Hormone Releasing Hormone via Ras, Raf, and Mitogen-Activated Protein Kinase

Abstract

Although GHRH has previously been shown to regulate proliferation of breast cancer cells and prevent apoptosis, the intracellular pathways mediating this effect have not been clarified. Exogenous GHRH stimulated a dose-dependent proliferative response within 24 h in MDA-231, as well as in T47D cells and in MCF-7 cells transfected with the GHRH receptor. The proliferation of MDA-MB-231 (MDA-231) cells was associated with an increase in tritiated thymidine uptake. In addition, phosphorylation of MAPK was rapidly stimulated by GHRH. The phosphorylation of MAPK by GHRH was prevented by transfection of the cells with dominant-negative Ras or Raf or by pretreatment of cells with Raf kinase 1 inhibitor. The inhibition of Ras and Raf, as well as the inhibition of MAPK phosphorylation by PD98059, also prevented GHRH-induced cell proliferation. Finally, pretreatment of cells with the somatostatin analog, BIM23014, also prevented GHRH-induced MAPK phosphorylation and cell proliferation. These results indicate that GHRH stimulates dose-dependent cell proliferation of MDA-231 breast cancer cells through a pathway that requires Ras, Raf, and MAPK phosphorylation. The results also provide support for a possible autocrine/paracrine antagonism between GHRH and somatostatin in the regulation of MDA-231 cell population maintenance. Taken together, the studies provide further insight into the possible role of GHRH as a growth factor in breast cancer.

Triple-negative breast cancers express receptors for growth hormone-releasing hormone (GHRH) and respond to GHRH antagonists with growth inhibition

“…Results by Siriwardana et al [39] indicate that GHRH stimulates cell proliferation of MDA-MB-231 breast cancer cells through a pathway that requires MAP-kinase phosphorylation via the Ras/Raf-kinase signal transduction pathway, and in line with these findings, we observed that stimulation with GHRH induced a threefold increase of phosphorylation of the MAP-kinases ERK1/2.…”

“…Although the post receptor mechanisms of tumoral GHRH receptors is not fully elucidated, recent studies demonstrate that growth stimulation by GHRH requires the Ras/Raf signaling pathway and the activation of MAPkinases in estrogen/progesterone negative HER2 overexpressing MDA-MB-231 breast cancer cells [39].…”

Rainbow trout somatostatin receptor subtypes SSTR1A, SSTR1B, and SSTR2 differentially activate the extracellular signal-regulated kinase and phosphatidylinositol 3-kinase signaling pathways in transfected cells

“…The involvement of ERK in conducting SS intracellular signaling also has been studied in mammalian systems, but the nature of the response appears cell line specific. For example, in human A431 cells, SS increased ERK activation (Stetak et al 2001), whereas in human MDA-231 cells, SS decreased ERK activation (Siriwardana et al 2006). Interestingly, in mouse MIN6 cells, SS has a dual effect on ERK activity, with an initial PTX-independent ERK activation followed by a later partially PTX-sensitive inhibition of ERK (Yoshitomi et al 1997).…”

Differential expression of GHRH receptor and its splice variant 1 in human normal and malignant mucosa of the oesophagus and colon

“…Cyclin D1 is elevated in cells expressing GHRH-R and SV-1 after exposure to GHRH (7). GHRH-R and conceivably SV-1 receptor share the intracellular part and operate by mechanisms that involve the activation of Ras signalling (15,18). Cyclin D1 is a well established target of activation of Ras signalling, which has been shown to be down-regulated by antagonists of GHRH in experimental lung carcinomas (6).…”