Examining the role of protein phosphatase 5 in the DNA damage and neuronal signaling pathways by identification of targets and protein partners
Protein phosphatase 5 (PP5) is a member of the phosphoprotein phosphatase (PPP) family of serine/threonine phosphatases. PP5 has an N-terminal domain consisting of three tetratricopeptide repeats (TPR) and a C-terminal phosphatase domain. PP5 is ubiquitously expressed in all mammalian tissues examined and has a low basal activity due to inhibitory interaction between the TPR and catalytic domains of the enzyme. PP5 has been implicated in a variety of cellular processes, including cell cycle arrest and repair in response to DNA damage, glucocorticoid receptor (GR) signaling, cell growth and differentiation, and regulation of ion channels. However, the mode of activation of PP5 in many of these pathways is yet to be determined. The major objective of this study was to increase our understanding of the role of PP5 in the DNA damage pathway as well as in glucocorticoid receptor-mediated neuronal signaling and to identify targets and binding partners of PP5 in these pathways. Using a label-free phosphoproteomics approach, 6 potential targets of PP5 in the DNA damage pathway were identified of which 4 proteins, including Ybox-binding protein (YB-1), Lamin A/C, apoptotic chromatin condensation inducer in the nucleus (Acinus) and ribosomal protein S6, are known to be involved in the DNA damage response. Investigation of the functional relationship between PP5 and GR revealed that both proteins are co-localized at the cellular level in neurons and can be isolated in a complex from rat brain extracts. Mass spectrometric analysis of PP5 immune complexes from rat brain identified several known proteins including heat shock protein 90 (Hsp90) and GRs. Several novel putative binding partners of PP5 were identified, that include PKA regulatory subunits RIIα and RIIβ, dopamine and adenosine 3’:5’ -monophosphate-regulated phosphoprotein (DARPP32), synapsin and chaperonin containing TCP-1 (CCT) molecular chaperone subunits among others, suggesting additional functional roles for PP5 in neurons. Functional analysis of the association of PP5 with the proteins identified in this study may provide new insights into the regulation of PP5 in neurons.
Rossie, Purdue University.
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