Tyrosine Phosphorylation of p34cdc2 Is Regulated by Protein Phosphatase 2A in Growing Immature Xenopus Oocytes

1995 ◽  
Vol 219 (1) ◽  
pp. 29-38 ◽  
Author(s):  
Hélène Rime ◽  
Catherine Jessus ◽  
René Ozon
Keyword(s):  
Tyrosine Phosphorylation ◽  
Protein Phosphatase ◽  
Xenopus Oocytes ◽  
Protein Phosphatase 2A ◽  
Phosphatase 2A

scholarly journals Role of Protein Phosphatase-2A (PP-2A) in the Control of Mitosis and Meiosis.

2020 ◽  
Author(s):  
H.Y. Lim Tung ◽  
H.Y. Lim Tung ◽  
H.Y. Lim Tung ◽  
H.Y. Lim Tung ◽  
H.Y. Lim Tung ◽  
...  
Keyword(s):  
Meiotic Division ◽  
Protein Phosphatase ◽  
Xenopus Oocytes ◽  
Protein Phosphatase 2A ◽  
Scientific Evidence ◽  
Specific Inhibitor ◽  
Phosphatase 2A ◽  
Greatwall Kinase ◽  
Mitosis And Meiosis

A specific form of Protein Phosphatase-2A (PP-2A), namely PP2A-B55δ was proposed to occupy a central role in the control of mitosis entry and exit, and meiosis in Xenopus oocytes [1,3]. It was held that PP2A-B55δ is responsible for dephosphorylating substrates of cdc2/Cdk1 and that inhibition of PP2A-B55δ by Arpp-19 phosphorylated at serine 67 by Greatwall kinase triggers entry of both mitosis and meiosis in Xenopus oocytes. It was further declared that the phosphorylation of Arpp19 at serine 109 by PKA underlies the blockade of meiotic division and that dephosphorylation of serine 109 of Arpp19 triggers resumption of meiotic division in Xenopus oocytes [4]. Recently two groups have stated that PP2A-B55δ is the protein phosphatase that is responsible for dephosphorylating both serine 67 and serine 109 of Arpp19 [4,5] However, unfortunately for the authors concerned [1-5], no verifiable scientific evidence exists that shows that Arpp19 is a specific inhibitor of PP-2AB55ɗ when Arpp19 is phosphorylated at serine 67 by Greatwall kinase and that Arpp-19 phosphorylated at serine 67 and Arpp19 phosphorylated at 109 are both specifically dephosphorylated by PP-2AB55ɗ Arpp19. The idea that Arpp-19 phosphorylated at serine 67 is both an inhibitor and a substrate of PP-2AB55ɗ has more to do with science fiction than science. The role of other Protein Phosphatases, including, PP-2A-B'56ɗ and Protein Phosphatase-1 I (PP-1 I ) cannot be ignored. Evidenceis presented and discussed here..

scholarly journals Role of Janus kinase-2 in insulin-mediated phosphorylation and inactivation of protein phosphatase-2A and its impact on upstream insulin signalling components

1999 ◽  
Vol 344 (3) ◽  
pp. 895-901 ◽  
Author(s):  
Najma BEGUM ◽  
Louis RAGOLIA
Keyword(s):  
Tyrosine Phosphorylation ◽  
Protein Phosphatase ◽  
Insulin Treatment ◽  
Insulin Signalling ◽  
Protein Phosphatase 2A ◽  
Catalytic Subunit ◽  
Janus Kinase ◽  
Receptor Protein ◽  
Phosphatase 2A

Our recent studies indicate that insulin rapidly inactivates serine/threonine protein phosphatase-2A (PP-2A) by increasing tyrosine phosphorylation on the catalytic subunit. The exact mechanism of PP-2A inactivation by insulin in vivo is unclear. The Janus kinase (JAK) family of non-receptor protein tyrosine kinases constitute a novel type of signal-transduction pathway which is activated in response to a wide variety of polypeptide ligands, including insulin. In this study we investigated the potential role of JAK-2 in insulin-mediated tyrosine phosphorylation and inactivation of PP-2A using the rat skeletal muscle cell line L6. Co-immunoprecipitation studies revealed that PP-2A is associated with JAK-2 in the basal state. Insulin treatment did not alter JAK-2 association with PP-2A, but did increase JAK-2-mediated tyrosine phosphorylation of the PP-2A catalytic subunit and therefore inhibited PP-2A enzymic activity. Furthermore, PP-2A is associated with phosphoinositide 3-kinase (PI-3K) in the basal state and insulin treatment increases the catalytic activity of PI-3K bound to PP-2A. Pretreatment with AG-490, a specific JAK-2 inhibitor, and SpcAMP, a cAMP agonist, prevented the insulin-mediated increase in (i) JAK-2 kinase activity, (ii) PP-2A tyrosine phosphorylation, (iii) PP-2A inactivation and restored the enzyme activity to control levels, and (iv) PP-2A and JAK-2-associated PI-3K activity. These observations, together with the fact that insulin rapidly activates JAK-2 in L6 cells, and that this is accompanied by an increase in tyrosine phosphorylation of PP-2A in JAK-2 immunoprecipitates, suggest that insulin controls the activation status of PP-2A by tyrosine phosphorylation via JAK-2. PP-2A inactivation may result in an amplification of insulin-generated signals at the level of PI-3K.

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