LSJL may inhibit Src activation in chondrocytes

This isn’t a breakthrough study but it’s always nice to see a new LSJL study coming out.

Distinctive Subcellular Inhibition of Cytokine-Induced Src by Salubrinal and Fluid Flow.

“A non-receptor protein kinase Src plays a crucial role in fundamental cell functions such as proliferation, migration, and differentiation. Inhibition of Src is reported to contribute to chondrocyte homeostasis. In response to inflammatory cytokines and stress to the endoplasmic reticulum (ER) that increase proteolytic activities in chondrocytes, we addressed two questions: Do cytokines such as interleukin 1 beta (IL1β) and tumor necrosis factor alpha (TNFα) induce location-dependent Src activation? Can cytokine-induced Src activation be suppressed by chemically alleviating ER stress or by applying fluid flow? Using live cell imaging with two Src biosensors (i.e., cytosolic, and plasma membrane-bound biosensors) for a fluorescence resonance energy transfer (FRET) technique, we determined cytosolic Src activity as well as membrane-bound Src activity in C28/I2 human chondrocytes. In response to TNFα and IL1β, both cytosolic and plasma membrane-bound Src proteins were activated, but activation in the cytosol occurred earlier than that in the plasma membrane. Treatment with salubrinal or guanabenz, two chemical agents that attenuate ER stress, significantly decreased cytokine-induced Src activities in the cytosol, but not in the plasma membrane. fluid flow reduced Src activities in the plasma membrane, but not in the cytosol. Src activity is differentially regulated by salubrinal/guanabenz and fluid flow in the cytosol and plasma membrane.”

Interesting that fluid flow reduced Src activation in the plasma membrane but the Cytosol and for Salubrinal it was vice versa.  The plasma membrane is the outside covering of the cell so it makes sense to be more affect by fluid flow as it would be in direct contact with it.  Whereas cytosol is the fluid on the inside of the cell. It would be highly significant if we could identify that LSJL mainly affected proteins in the plasma membrane but not so much the cytosol.

“Src is one of the integrin-dependent signaling proteins involved in mechanotransduction, and it plays critical roles in various cellular processes including proliferation, apoptosis, migration, adhesion, and differentiation. To mediate such a variety of cellular processes, Src’s distinct subcellular activation pattern is required. Src is mainly stationed in the cytosol near the endosomes, and activation of Src requires its translocation to the plasma membrane through the cytoskeleton”

“the shear stress of 2–10 dynes/cm2 has been shown to affect chondrocyte signaling and metabolism either positively or negatively”

“Cells were pretreated with Cytochalasin D (CytoD) for 1 h to disrupt the actin cytoskeleton or with MβCD for 1 h to extract cholesterol from the plasma membrane. CytoD partially blocked Cyto-Src activation, and it completely inhibited Lyn-Src activation. MβCD reduced both Cyto-Src and Lyn-Src activations, although to a lesser degree to Cyto-Src. Collectively, these data suggest that the actin cytoskeleton and lipid rafts are essential components for cytokine-induced Lyn-Src activation”

“Lyn-Src was responsive to fluid flow in a magnitude-dependent manner. In response to shear stress at 5 dynes/cm2, a rapid inhibition of Lyn-Src activity was observed (9.7% decrease). In contrast, shear stress at 10 dynes/cm2 led to its activation (14.9% increase). However, Cyto-Src activity was not altered at any magnitude of shear stress”

According to one article, inhibition of Src kinase activates the chondrocyte phenotype.  The article however did not distinguish between Src activities in the cytoplasma or plasma membrane.  It’s possible for instance that only Src activities in the cytoplasm discourage the chondrogenic phenotype and fluid flow would therefore have no effect.

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