Protein kinases and phosphatases regulate the activity of extracellular signal‐regulated kinases 1 and 2 (ERK1/2) by controlling the phosphorylation of specific residues. We report the physical and functional association of ERK1/2 with the PTP‐SL and STEP protein tyrosine phosphatases (PTPs). Upon binding, the N‐terminal domains of PTP‐SL and STEP were phosphorylated by ERK1/2, whereas these PTPs dephosphorylated the regulatory phosphotyrosine residues of ERK1/2 and inactivated them. A sequence of 16 amino acids in PTP‐SL was identified as being critical for ERK1/2 binding and termed kinase interaction motif (KIM) (residues 224–239); it was shown to be required for phosphorylation of PTP‐SL by ERK1/2 at Thr253. Co‐expression of ERK2 with catalytically active PTP‐SL in COS‐7 cells impaired the EGF‐induced activation of ERK2, whereas a PTP‐SL mutant, lacking PTP activity, increased the ERK2 response to EGF. This effect was dependent on the presence of the KIM on PTP‐SL. Furthermore, ERK1/2 activity was downregulated in 3T3 cells stably expressing PTP‐SL. Our findings demonstrate the existence of a conserved ERK1/2 interaction motif within the cytosolic non‐catalytic domains of PTP‐SL and STEP, which is required for the regulation of ERK1/2 activity and for phosphorylation of the PTPs by these kinases. Our findings suggest that PTP‐SL and STEP act as physiological regulators of the ERK1/2 signaling pathway.

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...

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