CELLULAR AND MOLECULAR CHARACTERIZATION OF A BRAIN-ENRICHED PROTEIN-TYROSINE-PHOSPHATASE

Regional variations in the expression of a striatal enriched protein t yrosine phosphatase called STEP were studied in the adult rat brain by a combination of immunocytochemistry, lesion studies, Western blottin g, and in situ hybridization. Monoclonal antibodies generated against STEP identified multiple polypeptides of M(r) 46, 37, 33 and a doublet of M(r) 64-66 kDa on Western blots. Although the three STEP immunorea ctive bands with lower molecular weights were enriched in cytosolic fr actions, the 64-66 kDa doublet was enriched in membrane fractions. mil of the immunoreactive forms were abundant in the caudate-putamen and were present in lower amounts or were undetectable in other brain regi ons. In substantia nigra, the M(r) 64-66 kDa doublet was not detected but bands with M(r) 46, 37, and 33 kDa were present. Immunocytochemica l and lesion experiments demonstrated that the cytosolic STEP isoforms present in the substantia nigra are in presynaptic axons originating from the projection neurons of the caudate putamen, which innervate th is structure. Additional in situ hybridization studies showed that STE P mRNA expression patterns correlate with the patterns of immunocytoch emical staining. These findings indicate that there are multiple polyp eptide isoforms of STEP enriched In the basal ganglia and related stru ctures which differ in terms of their intracellular locations and func tional roles.