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Placental lactogen in breast cancer

Tuttle, Traci R.
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378196610

Abstract Details

2013, PhD, University of Cincinnati, Medicine: Cancer and Cell Biology.
Human placental lactogen (hPL) is a pregnancy specific hormone and a member of the family of human lactogens, which also includes human growth hormone (hGH) and human prolactin (hPRL), all of which activate the prolactin receptor (PRLR). An identical hPL protein is coded for by two genes, CSH1 and CSH2. Several studies have reported detection of hPL protein in breast carcinomas and sera from breast cancer patients. Previous studies in our laboratory found that treatment with exogenous hPRL protected breast cancer cell lines (BCC) from cytotoxicity by chemotherapeutic drugs. We hypothesized that hPL is produced by breast cancer cells, acts as an autocrine survival factor and can serve as a biomarker for the disease. Our objectives were to: a) examine expression of CSH genes in BCC, breast carcinomas and normal breast tissue by real-time and conventional PCR, b) generate and validate antibodies against hPL and develop assays for detecting hPL protein, c) determine whether hPL protein is produced by BCC, primary breast tumors or normal breast tissue, by western blotting, ELISA and immunohistochemistry, and d) examine whether exogenous hPL protects BCC from cytotoxicity caused by chemotherapeutic drugs. We found that CSH1 and CSH2 were expressed in BCC, and that several monoclonal and polyclonal antibodies detected a protein 2-3 kDa larger than recombinant or placental hPL by western blotting. The larger protein was believed to be a post-translationally modified hPL variant, or `hPL’. In addition, two monoclonal antibodies against hPL positively stained several primary breast carcinomas, but not normal breast tissue. Using a bioassay and a sandwich ELISA which I developed, I measured a protein that I believed to be hPL in conditioned medium from BCC. Treatment of selected BCC with exogenous hPL protected the cells from the cytotoxicity caused by cisplatin, doxorubicin and taxol. After generating two additional monoclonal antibodies, we found that they did not detect hPL protein in lysates from BCC or primary carcinomas, but detected recombinant and placental-derived hPL. However, overexpression of CSH1 in BCC resulted in a product identical in size to placental hPL, indicating that it is not post-translationally modified. Suppression of CSH expression by shRNA in BCC did not decrease `hPL’, indicating that most previously used antibodies are non-specific for hPL. In conclusion, we have shown that expression of CSH mRNA in breast cancer does not predict detectable levels of hPL protein. hPL protein was detectable in BCC only when highly overexpressed, indicating a post-transcriptional inhibitory mechanism that can be overcome by large amounts of message. If this inhibitory mechanism is reversible under certain circumstances, autocrine hPL, like exogenous hPL, could act as a pro-survival factor for these cells. The slightly larger protein recognized by many antibodies and dubbed `hPL’ has not been identified, but must bear significant structural similarity to hPL.
Nira Ben-Jonathan, Ph.D. (Committee Chair)
Scott Belcher, Ph.D. (Committee Member)
Kenneth Greis, Ph.D. (Committee Member)
Shuk-Mei Ho, Ph.D. (Committee Member)
Susan Waltz, Ph.D. (Committee Member)
169 p.
Molecular Biology
breast cancer; placental lactogen; prolactin receptor; antibodies; expression

Recommended Citations

Citations

  • Tuttle, T. R. (2013). Placental lactogen in breast cancer [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378196610

    APA Style (7th edition)

  • Tuttle, Traci. Placental lactogen in breast cancer. 2013. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378196610.

    MLA Style (8th edition)

  • Tuttle, Traci. "Placental lactogen in breast cancer." Doctoral dissertation, University of Cincinnati, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378196610

    Chicago Manual of Style (17th edition)

ucin1378196610
553
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