Journal of Blood Disorders & Transfusion

Abstract

Phosphorylation State of S6K1 is Redundant for its Blood Interaction with F Actin

Shafat A Latoo* and Khurshid I Andrabi

The evolutionarily conserved kinase (S6K1) that is actuated in response to certain stimulants like insulin, amino acids and several other growth factors has emerged as a major effector of growth and proliferation of blood cells. In certain types of cancers, the S6K1 a serine/threonine kinase is constantly actuated and acts as a downstream effector of the Akt/phosphatidylinositol 3-kinase pathway. S6K1 serves to cross-link actin filament and activates the Rho family of Guanosine Triphosphate (GTPases). We here present the evidence for domain-specific interaction of S6 kinase 1 (S6K1) with filamentous actin or F actin. We showed for the first time that the [ΔNH_2-146/ΔCT₂₄₀ a. acid] region of S6K1 is responsible for its discrete binding to F actin. We also demonstrate that S6K1 binding to filamentous actin is phosphorylation independent and not facilitated by any other protein rather than direct interaction and we couldn’t observe any interaction of S6K1 for monomeric actin (G actin). By a time course experiment, we could found that the kinetics of spontaneous actin polymerization is not affected by the presence of S6K1 rather it enforces stability in F actin by cross-linking it and rendering it more stable in the form of multifilament bundled actin. Using electron microscopy we found that these closely packed bundles were often somewhat curved, which could suggest pliable cross-linking. We further observe that S6 kinase 1 persists to show reactivity towards filamentous actin that stands unaltered amid deletions compromised for [ΔNH_2-146/ΔCT₁₀₄] or [ΔNH_2-46]/ΔCT₁₀₄] or [ΔNH_2-146] or [ΔNH_2-46] or [ΔCT₁₀₄]. By computational study, we found that the [ΔNH_2-146/ΔCT₂₄₀ a. acid] region of S6K1 is rich in hydrophobic amino acids and holds primarily coiled-coil and alpha-helical structure which serves as a structural basis for some of the actin-binding proteins. These data together with the capability of S6K1 to attach filamentous actin indicate that binding is phosphorylation independent, direct, and facilitated by the [ΔNH_2-146/ΔCT₂₄₀ a. acid] region of S6K1.

Published Date: 2023-09-27; Received Date: 2023-08-21