Identification, primary structure, and distribution of CLA-1, a novel member of the CD36/LIMPII gene family

Abstract

The thrombospondin and collagen type I receptor CD36 is a plasma membrane glycoprotein present in a restricted number of cell types. By contrast, rat lysosomal integral membrane protein II (LIMPII) is expressed on the membrane of lysosomes in all cell types so far examined. Nevertheless, both belong to the same gene family based on alignment of their respective amino acid sequences. To explore the existence of other related members, we have used the polymerase chain reaction with primers derived from highly conserved amino acid regions between CD36 and rat LIMPII. A human cDNA corresponding to a novel member of this family has been identified and isolated. This new member has been designated as CD36 and LIMPII Analogous-1 (CLA-1). Human CLA-1 cDNA predicts a protein 409 amino acids long with a 20% amino acid identity with CD36 and rat LIMPII. Further studies revealed that the sequenced cDNA clone may result by alternative splicing from a longer mRNA form having an insertion of 300 nucleotides located 126 nucleotides downstream from the initiation codon of cloned CLA-1. This form would encode a protein 509 amino acids long, whose sequence matches without any long gap to amino acid sequences of CD36 and rat LIMPII. Northern blot analysis indicates that CLA-1 is widely expressed although its mRNA steady state levels vary considerably among the analyzed cell types. Transient transfection experiments of a CD36-CLA-1 chimera, constructed by replacing the carboxyl cytoplasmic tail of CD36 for the carboxyl cytoplasmic tail of CLA-1, suggest that native CLA-1 protein is found on the plasma membrane.