Molecular Cloning, Genomic Organization, and Expression of a Testicular Isoform of Hormone-Sensitive Lipase

By catalyzing the rate-limiting step in adipose tissue lipolysis, hormone-sensitive lipase (HSL) is an important regulator of energy homeostasis. The role and importance of HSL in tissues other than adipose are poorly understood. We report here the cloning and expression of a testicular isoform, designated HSL_tes. Due to an addition of amino acids at the NH₂-termini, rat and human HSL_tesconsist of 1068 and 1076 amino acids, respectively, compared to the 768 and 775 amino acids, respectively, of the adipocyte isoform (HSL_adi). A novel exon of 1.2 kb, encoding the human testis-specific amino acids, was isolated and mapped to the HSL gene, 16 kb upstream of the exons encoding HSL_adi. The transcribed mRNA of 3.9 kb was specifically expressed in testis. No significant similarity with other known proteins was found for the testis-specific sequence. The amino acid composition differs from the HSL_adisequence, with a notable hydrophilic character and a high content of prolines and glutamines. COS cells, transfected by the 3.9-kb human testis cDNA, expressed a protein of the expected molecular mass (M_r≈ 120,000) that exhibited catalytic activity similar to that of HSL_adi. Immunocytochemistry localized HSL to elongating spermatids and spermatozoa; HSL was not detected in interstitial cells.