Catalytic Activity Is Required for Calcium/Calmodulin-dependent Protein Kinase IV to Enter the Nucleus

Abstract

Calcium/calmodulin-dependent protein kinase IV (CaMKIV) is a nuclear protein kinase that responds to acute rises in intracellular calcium by phosphorylating and activating proteins involved in transcription. Consistent with these roles, CaMKIV is found predominantly in the nucleus of cells in which it is expressed. Here we evaluate nuclear entry of CaMKIV and demonstrate that the protein kinase homology domain is both necessary and sufficient for nuclear localization. Unexpectedly, although catalytic activity is required for nuclear translocation, it is not required for CaMKIV to interact with the nuclear adaptor protein, importin-␣. Because the catalytically inactive molecules remain in the cytoplasm, these data suggest that this interaction is not sufficient for nuclear entry. We evaluated a role for other proteins known to interact with CaMKIV in regulation of its nuclear entry. Although our data do not support a role for calmodulin or protein phosphatase 2A, the catalytically inactive CaMKIV proteins interact more avidly with CaM-dependent protein kinase kinase (CaMKK), which is restricted to the cytoplasm. We find that the catalytically inactive proteins do not inhibit nuclear entry of wild-type CaMKIV but do inhibit the ability of the wild-type protein kinase to stimulate cyclic AMP response element-binding protein-mediated tran-

Cytoplasmic localization of calcium/calmodulin-dependent protein kinase I-$alpha; depends on a nuclear export signal in its regulatory domain

“…The current study demonstrates that activity alone cannot account for the localization of CaMKI-a, since inactivation of the kinase by mutation of K 49 or activation with KCl or ionomycin did not significantly affect localization. This contrasts with recent studies of CaMKIV, whose catalytic activity is needed for nuclear entry [32].…”

“…Import of NLS-cargo is mediated by importin-a, which binds to the NLS and then forms a complex with importin-b that carries the cargo through the nuclear pore [35]. CaMKI-a does not appear to bind to importin-a in vitro [32]. Thus, CaMKI-a may interact with other members of the nuclear import machinery or may enter the nucleus coupled to other NLS-cargo(s).…”

CRP1, a Protein Localized in Filopodia of Growth Cones, Is Involved in Dendritic Growth

“…7D). The role of CaMKIV was confirmed by using a dominant-negative form of CaMKIV (Lemrow et al, 2004), which blocked the upregulation of CRP1 mRNA levels induced by KCl (Fig. 7E).…”

TRPC6 channels promote dendritic growth via the CaMKIV-CREB pathway

“…Since activation of CaMKIV is required for dendritic growth (Redmond et al, 2002), we asked whether TRPC6 affected dendritic growth through activation of CaMKIV. To address this question, we transfected hippocampal cultures with wild-type TRPC6 and CaMKIV-T200A (DNCaMKIV), which is a dominant-negative mutant of CaMKIV (Lemrow et al, 2004 (Yu and Malenka, 2003) rescued the change in phenotype induced by TRPC6 shRNAi. Transfection of TRPC6 shRNAi showed impaired dendritic arbors compared with control vectors (Fig.…”