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 t yrosine kinase, is an important regulator of germ cell development in rodent gonads. However, no information about the role of KL in the ova ries of women or higher primates has been available. We studied the ex pression of KL messenger RNA (mRNA) in human ovaries and the effect of purified hCG and recombinant human FSH (rhFSH) on KL mRNA steady stat e levels in cultures of human granulosa-luteal (GL) cells obtained at oocyte harvest for in vitro fertilization. KL complementary DNA was ge nerated 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 ob served in GL cells and ovarian tissue. In Northern blot analysis of hu man ovarian and GL cell RNA, a major transcript of approximately 6.0 k ilobases 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 gonadotropin s in a distinct time- and concentration-dependent manner. The KL mRNA levels of untreated and hCG- or rhFSH-stimulated GL cells were determi ned at 2- to 3-day intervals between days 2-10 of culture. An 8-h trea tment with hCG was shown to decrease KL mRNA levels on days 2, 3, 5, a nd 7 of culture, whereas rhFSH decreased KL mRNA levels on days 5 and 7 of culture. Time-course and concentration-dependence studies were pe rformed on days 2-7 of culture. Both gonadotropins decreased KL mRNA l evels as early as 2 h after treatment. The maximal response to hCG and rhFSH treatment was observed at 7-24 h. Concentration-dependence stud ies performed 8 or 24 h after treatment indicated that the maximal inh ibition occurred with 10-100 ng/ml hCG and 100-300 ng/ml rhFSH. We con clude that 1) the KL transcripts encoding 248- and 220-aa transmembran e proteins are expressed in vivo in the human ovary and in cultured hu man GL cells; and 2) KL transcript levels are rapidly decreased by gon adotropins in a time- and concentration-dependent manner in cultured G L cells. Thus, KL expression is hormonally regulated in human granulos a cells, and this growth factor may control the function of the ovaria n follicle during the human menstrual cycle.