engleski

OCRL phosphatase controls actin reorganization during the activation of human platelets spread on fibrinogen

Phosphatidylinositol-4, 5-bisphosphate [PI(4, 5)P2] is one of seven different phosphoinositides in the cell and is mostly localized at the plasma membrane. Its main functions are the regulation of endocytosis and actin reorganization. Lowe oculocerebrorenal syndrome protein (OCRL) dephosphorylates PI(4, 5)P2 on position five of the inositol ring resulting in the formation of PI4P. Mutations in OCRL cause Lowe syndrome which is characterized by congenital cataracts, central hypotonia, and renal proximal tubular dysfunction. In addition, an increased risk of bleedings was shown in some patients with Lowe syndrome. Blood platelets (PLT) have an important role in the hemostasis, at the site of the injury they recognize extracellular matrix proteins, become activated, and aggregate to prevent bleedings. We hypothesize that the loss of OCRL function leads to the changes in actin dynamics resulting in PLT dysfunction. Here, we show that pharmacological inhibition of OCRL in human PLTs spread on fibrinogen leads to an inhibition of full PLT activation shown by the reduced PLT spread area and the formation of actin-rich structures, called actin nodules. These actin nodules colocalize partially with vinculin and SNX9 and substantially with ARP2/3 complex, as well as with phosphotyrosine suggesting the impairment of the cytoskeletal reorganization during PLT activation. To investigate the role of OCRL-inhibition on signaling pathways we inhibited OCRL in PLTs and then activated them with thrombin. The Western blot analysis revealed reduced phosphorylation levels of myosin light chain (MLC), but not p38 or ERK. Our data suggest that OCRL might control actin cytoskeleton rearrangements during early steps of platelet activation and thus their proper function. Further experiments are underway to reveal the exact molecular mechanism in which OCRL controls actin reorganization in platelets.

OCRL, PI(4, 5)P2, platelets, Lowe syndrome

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