Although total Erk1/2 protein levels exhibited a cell type-specific and drug dose-dependent response similar to the one of α-tubulin and Hsp90, phosphorylated p44/42 levels were severely downregulated in all bladder cancer cell lines, implying the differential control between total and phosphorylated protein destabilization processes in response to the high drug dose treatments. This evidence concerns the gene HSP90AA1 and urinary bladder carcinoma.