Differential regulation of steroid hormone biosynthesis in R2C and MA-10 Leydig tumor cells: role of SR-B1-mediated selective cholesteryl ester transport.
The rat R2C Leydig tumor cell line is constitutively steroidogenic in nature, while the mouse MA-10 Leydig tumor cell line synthesizes large amounts of steroids only in response to hormonal stimulation. Earlier studies showed abundant cAMP-independent steroid production and constitutive expression of steroidogenic acute regulatory (StAR) protein in R2C cells. The objective of the current study was to identify possible genetic alterations in the R2C cell line responsible for rendering it a constitutively steroidogenic cell line, especially those that might have altered its cholesterol homeostatic mechanisms. Measurement of the levels of cholesterol esters and free cholesterol, precursors for steroidogenesis, indicated that R2C mitochondria were fourfold enriched in free cholesterol content compared with MA-10 mitochondria. In addition to the previously demonstrated increased expression of StAR protein, we show that R2C cells possess marginally enhanced protein kinase A activity, exhibit higher capacity to take up extracellular cholesterol esters, and express much higher levels of scavenger receptor-type B class 1 (SR-B1) and hormone sensitive lipase (HSL). These observations suggest that the high level of steroid biosynthesis in R2C cells is a result of the constitutive expression of the components involved in the uptake of cholesterol esters (SR-B1), their conversion to free cholesterol (HSL), and its mobilization to the inner mitochondrial membrane (StAR).
Rao
Rekha M
RM
Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA.
Jo
Youngah
Y
Leers-Sucheta
Susan
S
Bose
Himangshu S
HS
Miller
Walter L
WL
Azhar
Salman
S
Stocco
Douglas M
DM
D000818:Animals; D001483:Base Sequence; D001693:Biological Transport, Active; D003994:Bucladesine / Q000494:pharmacology; D018955:CD36 Antigens / Q000235:genetics / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism; D002788:Cholesterol Esters / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D007984:Leydig Cell Tumor / Q000235:genetics / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein / Q000378:metabolism*; D051116:Receptors, Scavenger; D051122:Scavenger Receptors, Class B; D013256:Steroids / Q000096:biosynthesis*; D002787:Sterol Esterase / Q000378:metabolism; D013736:Testicular Neoplasms / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D000098682:Steroidogenic Acute Regulatory Protein
D018955:CD36 Antigens; D002788:Cholesterol Esters; D008565:Membrane Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; C454739:Scarb1 protein, mouse; C495125:Scarb1 protein, rat; D051122:Scavenger Receptors, Class B; D013256:Steroids; D000098682:Steroidogenic Acute Regulatory Protein; D003994:Bucladesine; D002784:Cholesterol; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D002787:Sterol Esterase