Protein phosphatase-2A (PP-2A) is a major serine/threonine phosphatase abundantly expressed in eukaryotes. PP-2A is a heterotrimer that contains a 65 kD scaffold A subunit, a 36 kD catalytic C subunit, and a regulatory B subunit of variable isoforms ranging from 54-130 kDs. The scaffold subunits, PP2A-Aα/β, act as platforms for both the C and B subunits to bind, and thus are key structural components for PP-2A activity. Mutations in both genes encoding PP2A-Aα and PP2A-Aβ lead to carcinogenesis and likely other human diseases. Our previous work showed that the gene coding for PP2A-Aα is positively regulated by multiple transcription factors including Ets-1, CREB, and AP-2α but negatively regulated by SP-1/SP-3. In the present study, we have functionally dissected the promoter of the mouse PP2A-Aβ gene. Our results demonstrate that three major cis-elements, including the binding sites for Ets-1, SP1/SP3, and RXRα/β, are present in the proximal promoter of the mouse PP2A-Aβ gene. Gel mobility shifting assays reveal that Ets-1, SP1/SP3, and RXRα/β all bind to PP2A-Aβ gene promoter. In vitro mutagenesis and reporter gene activity assays demonstrate that while Ets-1 displays negative regulation, SP1/SP3 and RXRα/β positively regulate the promoter of the PP2A-Aβ gene. Co-expression of the cDNAs encoding Ets-1, SP1/SP3, or RXRα/β and the luciferase reporter gene driven by PP2A-Aβ promoter further confirm their control over the PP2A-Aβ promoter. Finally, ChIP assays demonstrate that Ets-1, SP1/SP3, and RXRα/β can all bind to the PP2A-Aβ gene promoter. Together, our results reveal that multiple transcription factors regulate the PP2A-Aβ gene. Moreover, our results provide important information explaining why PP2A-Aα and PP2A-Aβ display distinct expression levels.

The mammalian small ubiquitin-like modifiers (SUMOs) are actively involved in regulating differentiation of different cell types. However, the functional differences between SUMO isoforms and their mechanisms of action remain largely unknown. Using the ocular lens as a model system, we demonstrate that different SUMOs display distinct functions in regulating differentiation of epithelial cells into fiber cells. During lens differentiation, SUMO1 and SUMO2/3 displayed different expression, localization, and targets, suggesting differential functions. Indeed, overexpression of SUMO2/3, but not SUMO1, inhibited basic (b) FGF-induced cell differentiation. In contrast, knockdown of SUMO1, but not SUMO2/3, also inhibited bFGF action. Mechanistically, specificity protein 1 (Sp1), a major transcription factor that controls expression of lens-specific genes such as β-crystallins, was positively regulated by SUMO1 but negatively regulated by SUMO2. SUMO2 was found to inhibit Sp1 functions through several mechanisms: sumoylating it at K683 to attenuate DNA binding, and at K16 to increase its turnover. SUMO2 also interfered with the interaction between Sp1 and the coactivator, p300, and recruited a repressor, Sp3 to β-crystallin gene promoters, to negatively regulate their expression. Thus, stable SUMO1, but diminishing SUMO2/3, during lens development is necessary for normal lens differentiation. In support of this conclusion, SUMO1 and Sp1 formed complexes during early and later stages of lens development. In contrast, an interaction between SUMO2/3 and Sp1 was detected only during the initial lens vesicle stage. Together, our results establish distinct roles of different SUMO isoforms and demonstrate for the first time, to our knowledge, that Sp1 acts as a major transcription factor target for SUMO control of cell differentiation.transcription regulation | eye development | crystallin gene expression T he conjugation of small ubiquitin-like modifiers (SUMOs) to protein substrates (named sumoylation) is a critical posttranslational modification with diverse cellular functions (1). Three major SUMO isoforms (SUMO1, -2, and -3) were identified in vertebrates. Although the mature SUMO2 and SUMO3 share a very high level of sequence identity (97%) and cannot be immunologically discriminated (thus referred to as SUMO2/3), they significantly differ from SUMO1, with only 45% identity (2, 3). Recent studies using proteomics revealed that SUMO1 and SUMO2/3 can be targeted to both distinct and overlapping sets of substrates (4). However, whether SUMO1 and SUMO2/3 have redundant or different functions in vivo is not clear because inconsistent results have been reported in SUMO1 knockout mice (5, 6). SUMO conjugation is executed by three enzymes. The activating enzyme E1, a heterodimer of SAE1 and SAE2, transfers SUMO to the single E2-conjugating enzyme Ubc9, which either sumoylates the substrate alone, or cofunctions with different E3 ligases. Sumoylation is highly dynamic and can be rapidly reverted by sentrin-specific proteases (SE...

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DRD3 Ser9Gly polymorphisms are significantly associated with the therapeutic efficacy of pramipexole in Chinese patients with PD. A large-scale and multi-dose group study in patients with PD is necessary for evaluating the impact of the genetic polymorphisms of the dopamine receptor on the therapeutic effects of pramipexole.