Reflecting Back to Bring Nitric Oxide Research to the Laboratory.

Professor Ferid Murad has been a remarkable colleague and a mentor. During our very first meeting, he not only shared unresolved puzzles in Nitric Oxide (NO) research but also listened to my questions pointing to protein nitration and nitrosylation. This was start of a new avenue in my laboratory involving protein nitration, inducible nitric oxide synthase and nitrite production in the context of signaling and gene expression in cancer cells. Dynamic changes in the cytoskeleton remodeling in response to the cell membrane generated signals are regulated by p21-activated kinase 1 (PAK1) which also feed into microtubules (MT) dynamic via phosphorylating Tubulin Cofactor B (CoB) on serine 65 and serine 128. While While searching for the mechanism through which MT biogenesis might be counteracted for the purpose of maintaining the balance in MT dynamic, we explored the possibility of nitration of tyrosine residues in TCoB. We found that TCoB is nitrated on tyrosine 64 and tyrosine 98 and that nitrated TCoB inhibits TCoB phosphorylation and that intact PAK1 phosphorylation sites are also essential for the ability of TCoB to undergo nitration. We suggested a model wherein TCoB nitration acts as a feedback mechanism to counteract PAK1- signaling dependent microtubule dynamics, and thus, revealed an inherent regulatory coordination of growth factor and nitric oxide signaling in microtubule dynamics. In addition, cytoskeleton remodeling and NO production and resulting post-translational modifications in signaling modules serve as important modifiers of cellular processes. Here, I will discuss the cascade of events leading to my first meeting with Professor Murad, the development of scientific interactions, the recognition of our overlapping scientific interests in NO Signaling in cancer cells, and how these interactions have allowed us to connect NO - Cytoskeleton Signaling in cancer cells.