Abstract
Two-dimensional electrophoresis was used to detect a protein (ic) synthesized in rat corpus luteum cells in response to acute stimulation by human chorionic gonadotropin or dibutyryl cyclic AMP. This induced protein ic is isoelectric at pH 6.5 (isoelectric focusing) and has an apparent molecular weight of 28,000 (sodium dodecyl sulfate electrophoresis). The human chorionic gonadotropin or dibutyryl cyclic AMP dose response and time course of synthesis of the protein parallel those of progesterone synthesis in stimulated luteal cells. Additionally, cycloheximide, which inhibits the increase in progesterone formation caused by human chorionic gonadotropin or cAMP, also inhibits the synthesis of ic. Proteolytic polypeptide mapping suggests that ic has a very similar primary structure to another protein (pc), which has the same molecular weight as ic, differs from ic in pI, and is synthesized only in unstimulated cells. These polypeptide maps also demonstrate the close similarity of pc and ic to two proteins p and i, synthesized in control and in adrenocorticotropic hormone-stimulated rat adrenal cortex cells, respectively (Krueger, R. J. and Orme-Johnson, N. R. (1983) J. Biol. Chem. 258, 10159-10167). In both adrenal cortex and corpus luteum, binding of a tissue-specific polypeptide hormone acts via cAMP to cause increased steroidogenesis and induction of the synthesis of protein i (ic), with the same time course and hormone dose dependence. Also in both tissues, inhibition of protein synthesis at the level of translation (e.g. by cycloheximide addition) causes inhibition of i (ic) synthesis and of stimulated steroid production. This close correlation between the two different tissues in conditions which cause induction of the synthesis of these proteins suggests that the proteins may be common intermediaries in the control by polypeptide hormones of steroidogenesis in endocrine tissues.
Highlights
Two-dimensional electrophoresis was used to detect The initial and apparentIy rate-limiting sintepthperoduction a protein (i,) synthesized in ratcorpus luteum cellsin of steroid hormones in bothtissuesis the conversion of response to acute stimulationby human chorionic go- cholesterol’ to pregnenolone and isocaproaldehyde in reacnadotropin or dibutyryclyclic AMP
Inhibition of protein synthesis at the level of translation causes inhibitionof isynthesis andof stimulated steroid productionT.his close correlation between the two different tissues in conditions which cause induction of the synthesis of these proteins suggests that the proteinsmay be common intermediaries in the controbly polypeptide hormones of steroidogenesis in endocrinetissues
To extend and confirm these findings, we have studied the requirement for specific protein synthesis in 1)corpus luteum, a transitory endocrine organ which develops during ovarian follicular maturation and produces progesterone and estrogen, and 2) adipose tissue, a nonsteroidogenic tissue which, in response to peptide hormones, mobilizes and releases stored lipid in CAMP-mediated processes
Summary
From the Departmentof Biochemistry, Tufts University Health Sciences Campus, Boston,Massachusetts 02111. Two-dimensional electrophoresis was used to detect The initial and apparentIy rate-limiting sintepthperoduction a protein (i,) synthesized in ratcorpus luteum cellsin of steroid hormones in bothtissuesis the conversion of response to acute stimulationby human chorionic go- cholesterol’ to pregnenolone and isocaproaldehyde in reacnadotropin or dibutyryclyclic AMP This induced pro- tions catalyzed by the side-chain cleavage enzyme complex tein i,is isoelectric at pH 6.5 (isoelectric focusing) and [9,10,11,12]. Extramitochondrial mobilization of free cholesterol involves activation of hydrolysis in lipid droplets of cholesterol esters, which are derived primarily from serum lipoproteins, and transport of free cholesterol to the outer mitochondrial membrane [19,20,21,22] While each of these processes is stimulated by both the peptide hormone and second messenger, neither (process) is dependent upon ongoing protein synthesis. To extend and confirm these findings, we have studied the requirement for specific protein synthesis in 1)corpus luteum, a transitory endocrine organ which develops during ovarian follicular maturation and produces progesterone and estrogen, and 2) adipose tissue, a nonsteroidogenic tissue which, in response to peptide hormones, mobilizes and releases stored lipid in CAMP-mediated processes
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