IDENTIFICATION OF NOVEL HUMAN TUMOR CELL-SPECIFIC CAMK-II VARIANTS

CaMK-II (the (type II) multifunctional Ca2+/CaM-dependent protein kina se) has been implicated in diverse neuronal and non-neuronal functions , including cell growth control. CaMKII expression was evaluated in a variety of human tumor cell lines using RT-PCR (reverse transcriptase coupled polymerase chain reaction). PCR primers which flanked the CaMK -II variable domain were used so that all possible variants of the fou r mammalian CaMK-II genes (alpha, beta, gamma and delta) could be iden tified. 8 distinct CaMK-II isozymes were identified from human mammary tumor and neuroblastoma cell cDNA, each of which represented a varian t of beta, gamma or delta CaMK-II. They included 2 beta isozymes (beta (e), beta(e)'), 4 gamma isozymes (gamma(B), gamma(C), gamma(G), gamma( H)) and 2 delta isozymes (delta(C), delta(E)) This is the first report of human beta and delta CaMK-II sequences. A panel of human cell type s was then screened for these CaMK-II isozymes. As expected, cerebral cortex predominately expressed alpha, beta and delta, CaMK-II. In cont rast, tumor cells, including those of neuronal origin, expressed an en tirely different spectrum of CaMK-II isozymes than adult neuronal tiss ue. Tumor cells of diverse tissue origin uniformly lacked alpha CaMK-I I and expressed 1-2 beta isozymes, at least 3 gamma isozymes and 1-2 d elta isozymes. When compared to undifferentiated fibroblasts, beta(e), beta(e)', gamma(G), and gamma(H) were preferentially expressed in tum or cells. CaMK-II immunoblots also indicated that neuroblastoma and ma mmary tumor cells express isozymes of CaMK-II not present in their non -transformed cell or tissue counterpart. The identification of these n ew, potential tumor-specific CaMK-II variants supports previous indica tions that CaMK-II plays a role in growth control. In addition, these results provide insight into both splice variant switching and variabl e domain structural similarities among all CaMK-II isozymes.