EXPRESSION AND REGULATION OF THE LIPOPROTEIN-LIPASE GENE IN HUMAN ADRENAL-CORTEX

Lipoprotein lipase (LPL), an enzyme which hydrolyzes triglycerides and participates in the catabolism of remnant lipoproteins, plays a cruci al role in energy and lipid metabolism, The goal of this study was to analyze the expression and regulation of the LPL gene in human adrenal s, Reverse transcriptase-polymerase chain reaction amplification and s equence analysis demonstrated the presence of LPL mRNA in fetal and ad ult human adrenal cortex, Furthermore, the human adrenocortical carcin oma cell line, NCI-H295, expresses LPL mRNA and protein, which is loca lized to the outer cellular membrane as demonstrated by immunofluoresc ence confocal microscopy and can be released in the medium by heparin addition, To asses whether the LPL gene is regulated by agents regulat ing adrenal steroidogenesis, NCI-H295 cells were treated with activato rs of second messenger systems, Whereas the calcium-ionophore A23187 d id not affect LPL gene expression, treatment with phorbol 12-myristate 13-acetate decreased LPL mRNA levels in a time- and dose-dependent ma nner. This decrease after phorbol 12-myristate 13-acetate was associat ed with diminished heparin-releasable LPL mass and activity in the cul ture medium, Addition of the cAMP analog 8-Br-cAMP to NCI-H295 cells r esulted in a rapid, but transient dose-dependent induction of LPL mRNA , Treatment with the protein synthesis inhibitor cycloheximide gradual ly induced, whereas simultaneous addition of cAMP and cycloheximide su perinduced LPL mRNA levels, Nuclear run-on analysis indicated that the effects of cAMP and cycloheximide occurred at the transcriptional and post-transcriptional level, respectively, Transient co-transfection a ssays demonstrated that the first 230 base pairs of the proximal LPL p romoter contain a cAMP-responsive element activated by protein kinase A and transcription factors belonging to the CREB/CREM family, These d ata indicate that LPL is expressed in human adrenal cortex and regulat ed in NCI-H295 adrenocortical carcinoma cells by activators of the pro tein kinase A and protein kinase C second messenger pathways in a mann er comparable to P450sec, which catalyzes the first step in adrenal st eroidogenesis. These observations suggest a role for LPL in adrenal en ergy and/or lipid metabolism and possibly in steroidogenesis.