Two Distinct Tumor-Derived, Parathyroid Hormone-Like Peptides Result from Alternative Ribonucleic Acid Splicing

Abstract

A novel PTH-like peptide has recently been isolated and cloned from human tumors associated with the syndrome of humoral hypercalcemia of malignancy. The deduced product of the initial clones to be reported is a 177 amino-acid protein, consisting of a 36 amino-acid precursor sequence followed by a 141 amino-acid mature peptide. Southern analysis of genomic DNA is compatible with a single-copy gene, but Northern analysis of mRNAs from both tumors and normal tissues consistently reveals multiple hybridizing transcripts, suggesting the possibility of alternative RNA splicing. We provide here direct evidence of alternative RNA splicing by the identification of a second cDNA clone in a human renal carcinoma cDNA library. As compared to the initial clone, this cDNA contains a foreshortened 5'-untranslated region but is otherwise identical until the distal portion of the coding region, at which point it diverges completely to encode a 166 amino-acid mature peptide with 27 amino acids of unique C-terminal sequence. The relative lengths of the primary translation products encoded by these two cDNAs were confirmed by transcription and translation in vitro, and both products were shown to be processed by added microsomes. The unique 3'-ends of these two cDNAs, as well as that of a third cDNA isolated by another laboratory, were used to identify one or more hybridizing transcripts corresponding to each cDNA in mRNA from a human renal carcinoma as well as in mRNA from normal human keratinocytes. We conclude that alternative RNA splicing results in mRNAs which encode multiple PTH-like peptides.(ABSTRACT TRUNCATED AT 250 WORDS)