Increased CRMP2 phosphorylation in NPCs treated with HIV-gp120 protein, and rescue with CDK5 siRNA knockdown. Differentiating NPCs were transfected day 2 of differentiation with siRNA specific for CDK5 (siCDK5) or transfection reagent control, followed by treatment with recombinant HIV-gp120 protein (100 ng/mL) or vehicle control. Cells were fixed on day 4 of differentiation for double-immunolabeling analysis with antibodies against β-III Tubulin (immature neuronal marker) and pSer522-CRMP2 (pSer-CRMP2). (A-C) β-III Tubulin-positive NPC-derived neuronal progeny treated with vehicle control express background levels of pSer-CRMP2. (D-F) NPC-derived neuronal progeny treated with gp120 for 48 hrs display increased pSer-CRMP2 immunoreactivity in β-III Tubulin-positive cells. (G-I) β-III Tubulin-positive NPC-derived neuronal progeny treated with siCDK5 show low levels of pSer-CRMP2 immunoreactivity. (J-L) β-III Tubulin-positive NPC-derived neuronal progeny treated with siCDK5 and gp120 show background levels of pSer-CRMP2 immunoreactivity. (M, N) Semi-quantitative image analysis of β-III Tubulin (M) and pSer-CRMP2 (N) immunoreactivity. * p < 0.05 compared to vehicle-treated controls by one-way ANOVA with post-hoc Dunnett's test. Scale bar = 20 μm.