EXPRESSION AND CHARACTERIZATION OF SPLICE VARIANTS OF PYK2, A FOCAL ADHESION KINASE-RELATED PROTEIN

Focal adhesion kinase and the recently identified proline-rich tyrosin e kinase 2 (PYK2), also known as cell adhesion kinase beta, related ad hesion focal tyrosine kinase or calcium-dependent protein tyrosine kin ase, define a new family of non-receptor protein tyrosine kinases, Act ivation of PYK2 has been implicated in multiple signaling events, incl uding modulation of ion channels, T- and B-cell receptor signaling and cell death. Mechanisms underlying the functional diversity of PYK2 ar e unclear. Here, we provide evidence for two novel alternatively expre ssed isoforms of PYK2, One isoform, designated PYK2s (PYK2 splice form ), appears to he a splice variant of PYK2 lacking 42 amino acids withi n the C-terminal domain. A second isoform, referred to as PRNK (PYK2-r elated non-kinase), appears to be specified by mRNAs that encode only part of the C-terminal domain of PYK2, Northern blot analysis indicate s that the unspliced PYK2 is expressed at high levels in the brain and poorly expressed in the spleen, whereas PYK2s and PRNK are expressed in the spleen. In situ hybridization studies of rat brain demonstrate that the unspliced PYK2 is selectively expressed at high levels in hip pocampus, cerebral cortex and olfactory bulb, whereas PYK2s and PRNK a re expressed at low levels in all regions of rat brain examined, Immun ofluorescence analysis of ectopically expressed PRNK protein shows tha t PRNK, in contrast to full-length PYK2, is localized to focal adhesio ns by sequences within the focal adhesion targeting domain. In additio n, PYK2, but not PRNK, interacts with p130(cas) and Graf. These result s imply that PRNK may selectively regulate PYK2 function in certain ce lls by binding to some but not all PYK2 binding partners, and the func tional diversity mediated by PYK2 may be due in part to complex altern ative splicing.