Expression of c-kit ligand messenger ribonucleic acids in human ovaries and regulation of their steady state levels by gonadotropins in cultured granulosa-luteal cells.

The c-kit ligand (KL), a ligand for the c-kit protooncogene receptor tyrosine kinase, is an important regulator of germ cell development in rodent gonads. However, no information about the role of KL in the ovaries of women or higher primates has been available. We studied the expression of KL messenger RNA (mRNA) in human ovaries and the effect of purified hCG and recombinant human FSH (rhFSH) on KL mRNA steady state levels in cultures of human granulosa-luteal (GL) cells obtained at oocyte harvest for in vitro fertilization. KL complementary DNA was generated by reverse transcription-polymerase chain reaction from human ovarian tissue RNA. Two alternatively spliced KL transcripts encoding 248-amino acid (aa) and 220-aa membrane-associated KL proteins were observed in GL cells and ovarian tissue. In Northern blot analysis of human ovarian and GL cell RNA, a major transcript of approximately 6.0 kilobases was detected. Specific mRNA transcripts for KL were detected in dot blot filter hybridization analyses, and the steady state levels of these mRNAs were lowered in cultured GL cells by both gonadotropins in a distinct time- and concentration-dependent manner. The KL mRNA levels of untreated and hCG- or rhFSH-stimulated GL cells were determined at 2- to 3-day intervals between days 2-10 of culture. An 8-h treatment with hCG was shown to decrease KL mRNA levels on days 2, 3, 5, and 7 of culture, whereas rhFSH decreased KL mRNA levels on days 5 and 7 of culture. Time-course and concentration-dependence studies were performed on days 2-7 of culture. Both gonadotropins decreased KL mRNA levels as early as 2 h after treatment. The maximal response to hCG and rhFSH treatment was observed at 7-24 h. Concentration-dependence studies performed 8 or 24 h after treatment indicated that the maximal inhibition occurred with 10-100 ng/ml hCG and 100-300 ng/ml rhFSH. We conclude that 1) the KL transcripts encoding 248- and 220-aa transmembrane proteins are expressed in vivo in the human ovary and in cultured human GL cells; and 2) KL transcript levels are rapidly decreased by gonadotropins in a time- and concentration-dependent manner in cultured GL cells. Thus, KL expression is hormonally regulated in human granulosa cells, and this growth factor may control the function of the ovarian follicle during the human menstrual cycle.