ERK1 and ERK2 associate with the tyrosine phosphatase PTP-SL through a kinase interaction motif (KIM) located in the juxtamembrane region of PTP-SL. A glutathione S-transferase (GST)-PTP-SL fusion protein containing the KIM associated with ERK1 and ERK2 as well as with p38/HOG, but not with the related JNK1 kinase or with protein kinase A or C. Accordingly, ERK2 showed in vitro substrate specificity to phosphorylate GST-PTP-SL in comparison with GST-c-Jun. Furthermore, tyrosine dephosphorylation of ERK2 by the PTP-SL⌬KIM mutant was impaired. The in vitro association of ERK1/2 with GST-PTP-SL was highly stable; however, low concentrations of nucleotides partially dissociated the ERK1/2⅐PTP-SL complex. Partial deletions of the KIM abrogated the association of PTP-SL with ERK1/2, indicating that KIM integrity is required for interaction. Amino acid substitution analysis revealed that Arg and Leu residues within the KIM are essential for the interaction and suggested a regulatory role for Ser 231 . Finally, coexpression of PTP-SL and ERK2 in COS-7 cells resulted in the retention of ERK2 in the cytoplasm in a KIM-dependent manner. Our results demonstrate that the noncatalytic region of PTP-SL associates with mitogen-activated protein kinases with high affinity and specificity, providing a mechanism for substrate specificity, and suggest a role for PTP-SL in the regulation of mitogen-activated protein kinase translocation to the nucleus upon activation.
Extracellular signal-regulated kinases (ERKs)1 are serine/ threonine kinases of the MAP kinase family that are activated by a variety of growth and differentiation factors (1-4). ERK1/ 2-related kinases include members of the stress-and inflammation-activated MAP kinase subgroups, JNK/stress-activated protein kinase and p38/HOG (5-8). Differences in the response of ERK1/2 to activation agents have been postulated to account for the cell type-and stimulus-specific adaptive responses mediated by these kinases (9). For instance, inhibition of ERK1/2 function prevents proliferation of Chinese hamster ovary fibroblasts in response to growth-stimulating agents (10), and constitutive activation of the ERK1/2 pathway induces transformation of 3T3 fibroblasts (11,12). On the other hand, ERK1 and ERK2 also mediate the inhibition of cell growth arrest induced by nerve growth factor in 3T3 cells (13), and the differentiation of neuronal PC12 or erythroleukemia K562 cells is blocked by inhibition of the ERK1/2 pathway (11,14,15). Cytoplasmic activation of ERK1/2 requires the phosphorylation of both tyrosine and threonine regulatory residues, which is accomplished by the dual-specificity kinases MEK1 and MEK2 (16). Upon activation, ERK1 and ERK2 phosphorylate cytosolic and membrane-bound proteins, including signal transduction molecules and cytoskeletal components (1, 2). In addition, after stimulus-induced translocation to the nucleus, ERK1 and ERK2 phosphorylate and regulate the function of several transcription factors, thereby controlling the expression of specific responsive ge...