Myc oncoproteins are phosphorylated by casein kinase II.

Abstract

Casein kinase II (CK-II) is a ubiquitous protein kinase, localized to both nucleus and cytoplasm, with strong specificity for serine residues positioned within clusters of acidic amino acids. We have found that a number of nuclear oncoproteins share a CK-II phosphorylation sequence motif, including Myc, Myb, Fos, Ela and SV40 T antigen. In this paper we show that cellular myc-encoded proteins, derived from avian and human cells, can serve as substrates for phosphorylation by purified CK-II in vitro and that this phosphorylation is reversible. One-and two-dimensional mapping experiments demonstrate that the major phosphopeptides from in vivo phosphorylated Myc correspond to the phosphopeptides produced from Myc phosphorylated in vitro by CK-II. In addition, synthetic peptides with sequences corresponding to putative CK-II phosphorylation sites in Myc are subject to multiple, highly efficient phosphorylations by CK-11, and can act as competitive inhibitors of CK-II phosphorylation of Myc in vitro. We have used such peptides to map the phosphorylated regions in Myc and have located major CK-II phosphorylations within the central highly acidic domain and within a region proximal to the C terminus. Our results, along with previous studies on myc deletion mutants, show that Myc is phosphorylated by CK-II, or a kinase with similar specificity, in regions of functional importance. Since CK-II can be rapidly activated after mitogen treatment we postulate that CK-II mediated phosphorylation of Myc plays a role in signal transduction to the nucleus.

Cilostazol protects rat chondrocytes against nitric oxide–induced apoptosis in vitro and prevents cartilage destruction in a rat model of osteoarthritis

“…Although the role of PKCK2 is unknown, it may potentially participate in a complex series of cellular functions, including cell growth and proliferation, by catalyzing the phosphorylation of a large number of proteins (26). PKCK2 also participates in the regulation of apoptosis by phosphorylating some apoptosis-related factors (26)(27)(28)(29)(30)(31). Despite the many previous studies of PKCK2, little progress has been made in understanding its molecular role in chondrocytes.…”

Transformation by v-Myb

“…The importance of this deletion in oncogenesis is underscored by the high frequency with which a similar deletion occurs in murine leukemia virus-induced myeloid malignancies in mice (reviewed in Shen-Ong, 1990). In addition to the absence of much of the ®rst Myb repeat, v-Myb also lacks an amino terminal casein kinase II (CKII) phosphorylation site at residues 11 and 12 of c-Myb (Luscher et al, 1989) and an adjacent stretch of acidic residues. However, mutagenesis of this CKII site in cMyb does not cause e cient oncogenic transformation in cell culture or cancer in animals (Dini and Lipsick, Figure 1 v-Myb and c-Myb proteins.…”

Nuclear protein phosphorylation and growth control

“…CKII multiply phosphorylates c-Myc in vitro at two distinct regions, corresponding to amino acids 240-262 and 342-357 in the human c-Myc (Fig. 4; Luscher et al, 1989). [CKII has also been shown to phosphorylate similar sites on the N-Myc protein ].…”

“…[CKII has also been shown to phosphorylate similar sites on the N-Myc protein ]. These sites are also phosphorylated in vivo (Luscher et al, 1989) and lie, respectively, within an acidic central region (240-262), and a segment (342-357) flanking the basic DNA-binding domain (Fig. 4) Regions containing phosphorylation sites are expanded and the amino acid sequences given, together with the known enzymes which mediate the phosphorylation and dephosphorylation reactions.…”