STEP₆₁: A Member of a Family of Brain-Enriched PTPs Is Localized to the Endoplasmic Reticulum

Abstract

The STEP family of protein tyrosine phosphatases is highly enriched within the CNS. Members of this family are alternatively spliced to produce both transmembrane and cytosolic variants. This manuscript describes the distinctive intracellular distribution and enzymatic activity of the membrane-associated isoform STEP 61 . Transfection experiments in fibroblasts, as well as subcellular fractionations, sucrose density gradients, immunocytochemical labeling, and electron microscopy in brain tissue, show that STEP 61 is an intrinsic membrane protein of striatal neurons and is associated with the endoplasmic reticulum. In addition, structural analysis of the novel N-terminal region of STEP 61 reveals several motifs not present in the cytosolic variant STEP 46 . These include two putative transmembrane domains, two sequences rich in Pro, Glu, Asp, Ser, and Thr (PEST sequences), and two polyproline-rich domains. Like STEP 46 , STEP 61 is enriched in the brain, but the recombinant protein has less enzymatic activity than STEP 46 . Because STEP 46 is contained in its entirety within STEP 61 and differs only in the extended N terminus of STEP 61 , this amino acid sequence is responsible for the association of STEP 61 with membrane compartments and may also regulate its enzymatic activity.

The Striatal-Enriched Protein Tyrosine Phosphatase Gates Long-Term Potentiation and Fear Memory in the Lateral Amygdala

“…Alternative splicing of a single STEP gene produces a 46 kDa cytosolic member (STEP 46 ) and a 61 kDa membrane-associated member (STEP 61 ) (Bult et al, 1996). Lower molecular weight isoforms (STEP 38 and STEP 20 ) are also present in striatal tissue (Lombroso et al, 1993;Sharma et al, 1995).…”

“…These include two transmembrane domains, two polyproline domains, and two PEST sequences. Electron microscopy and biochemical analyses have localized STEP 61 to the endoplasmic reticulum and postsynaptic terminal, where it is associated both with the postsynaptic density (Bult et al, 1996;Boulanger et al, 1995;Oyama et al, 1995) and the N-methyl-D-aspartate (NMDA) receptor protein complex (Pelkey et al, 2002). STEP-family proteins contain an ERK binding domain, the kinase interacting motif (KIM), which is required for the association of STEP with the ERKs (Paul et al, 2003;Pulido et al, 1998).…”

Hypoxia‐Ischemia in Perinatal Rat Brain Induces the Formation of a Low Molecular Weight Isoform of Striatal Enriched Tyrosine Phosphatase (STEP)

“…Confirmation of this suggestion will require comparison of the sequence of the lower M r fragments produced under both conditions. STEP 61 is a transmembrane protein with the carboxyterminal phosphatase domain located intracellularly (Bult et al, 1996). Proteolytic cleavage of STEP 61 to produce STEP 33 would therefore result in the release of the phosphatase domain from the membrane.…”

“…The STEP 61 -pRC-CMV construct was produced as described elsewhere (Bult et al, 1996) and transfected into NT2/D1 cells as described (Nguyen et al, 1999). To determine the effect of calcium on STEP, transfected cells were treated with 10 M A23187 for 45 min before harvesting.…”

“…Subsequent studies have identified two subfamilies of STEP proteins: a group of higher molecular weight (M r ) isoforms that are enriched in membrane compartments, and a group of lower M r isoforms, some of which are membrane-associated and others of which are cytosolic proteins (Boulanger et al, 1995;Sharma et al, 1995;Bult et al, 1996Bult et al, , 1997.…”