Stimulation of proliferation of MCF-7 breast cancer cells by a transfected splice variant of growth hormone-releasing hormone receptor

doi:10.1073/pnas.0700407104

Stimulation of proliferation of MCF-7 breast cancer cells by a transfected splice variant of growth hormone-releasing hormone receptor

*Department of Biological Chemistry, University of Athens Medical School, 75 Micras Asias, 115 27 Athens, Greece; and
^†Endocrine Polypeptide and Cancer Institute, Veterans Affairs Medical Center and South Florida Veterans Affairs Foundation for Research and Education and Department of Pathology, University of Miami Miller School of Medicine, Miami, FL 33125

Contributed by Andrew V. Schally, January 19, 2007 (received for review October 10, 2006)

Abstract

Recent evidence indicates that growth hormone-releasing hormone (GHRH) functions as an autocrine/paracrine growth factor for various human cancers. A splice variant (SV) of the full-length receptor for GHRH (GHRHR) is widely expressed in various primary human cancers and established cancer cell lines and appears to mediate the proliferative effects of GHRH. To investigate in greater detail the role of SV1 in tumorigenesis, we have expressed the full-length GHRHR and its SV1 in MCF-7 human breast cancer cells that do not possess either GHRHR or SV1. In accordance with previous findings, the expression of both GHRHR and SV1 restored the sensitivity to GHRH-induced stimulation of cell proliferation, with SV1 being more potent than the GHRHR. Furthermore, MCF-7 cells transfected with SV1 proliferated more quickly than the controls, even in the absence of exogenously added GHRH, suggesting the existence of intrinsic, ligand-independent activity of SV1 after its transfection. In agreement with the stimulation of cell proliferation, the levels of proliferation markers cyclin D1, cyclin E, and proliferating cell nuclear antigen were elevated in MCF-7 cells treated with GHRH, cultured in both serum-free and serum-containing media. In addition, SV1 caused a considerable stimulation of the ability of MCF-7 cells to grow in semisolid medium, an assay considered diagnostic for cell transformation. Collectively, our findings show that the expression of SV1 confers oncogenic activity and provide further evidence that GHRH operates as a growth factor in breast cancer and probably other cancers as well.

Footnotes

^‡To whom correspondence may be addressed. E-mail: hkiaris{at}med.uoa.gr or andrew.schally{at}va.gov
Author contributions: A.V.S. and H.K. designed research; N.B., E.T., and S.K., performed research; N.B. and A.K. analyzed data; and N.B. and H.K. wrote the paper.
The authors declare no conflict of interest.
Abbreviations:

GH,

growth hormone;

GHRH,

GH-releasing hormone;

GHRHR,

GHRH receptor;

SV,

splice variant;

PCNA,

proliferating cell nuclear antigen.