HEART-TYPE FATTY-ACID-BINDING PROTEIN - INVOLVEMENT IN GROWTH-INHIBITION AND DIFFERENTIATION

Fatty acid binding proteins (FABPs) comprise a well-established family of cytoplasmic hydrophobic ligand binding proteins and are thought to be involved in lipid metabolism by binding and intracellular transpor t of long-chain fatty acids. However, from other studies role for FABP s in cell signalling, growth inhibition and differentiation has also b een implied. In particular, the heart-type (H-FABP) is abundantly expr essed in differentiated mammary gland and its relationship with a very homologous (95%) mammary derived growth inhibitor (MDGI) was disputed . Here we give a survey on the experimental evidence for the existence of such protein with growth inhibitory function. After cloning of the bovine adipocyte-type (A-)FABP cDNA from mammary gland we conclude th at the reported MDGI sequence actually represents a mixture of bovine H- and A-FABP and that the MDGI function is exerted by H-FABP. We also monitored the H-FABP level during differentiation of C2C12 muscle cel ls from myoblasts to multiply nucleated myotubes. H-FABP expression is clearly detected after that of the transcription factor myogenin whic h is upregulated immediately upon onset of differentiation and after t hat of the typical muscle enzyme creatine kinase. This argues against an active role of H-FABP in muscle development unlike the situation in the mammary gland.