Immunolocalization of PPP1C Isoforms in SH-SY5Y Cells During the Cell Cycle

Abstract

Phosphoprotein phosphatase 1 (PPP1) is the most widely expressed and abundant serine/threonine protein phosphatase. PPP1 regulates a variety of cellular functions such as glycogen metabolism, mitosis and meiosis, cell-cycle arrest, apoptosis, dynamics of actin cytoskeleton, protein synthesis among others. The versatility of the PPP1 catalytic subunit (PPP1C) is achieved by associating with different regulatory subunits that target PPP1C to a particular subcellular compartment determining its substrate specificity and activity. PPP1C is expressed in mammals in three isoforms: PPP1CA, PPP1CB and PPP1CC, each encoded by distinct genes. The PPP1C gene undergoes alternative splicing to originate PPP1CC1 and PPP1CC2 variants. PPP1A and PPP1C1 are expressed virtually in all tissues but are particularly enriched in the brain. The subcellular localization of the endogenous PPP1C isoforms is not fully elucidated, but all isoforms are found in the nucleus and cytoplasm, despite some isoform-specific differences in intranuclear distribution. Furthermore, it is known that PPP1 plays a key role in mitosis where PPP1C isoforms are differentially targeted to specific subcellular structures. However, in previous studies, non-neuronal cells were used as a model system to study PPP1 distribution during the cell cycle. In the studies here described, we used the neuronal-like cell line SH-SY5Y since PPP1 is a crucial protein in several neuronal functions.