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The up‐regulation of 14‐3‐3 proteins in Smad4 deficient epidermis and hair follicles at catagen

Each postnatal hair follicle (HF) perpetually goes through three phases: anagen, catagen, and telogen. The molecular signals that orchestrate the follicular transition between phases are still largely unknown. Our previous study shows that the keratinocyte specific Smad4 knockout mice exhibit progressive alopecia due to the mutant HFs failure to undergo programmed regression. To investigate the detailed molecular events controlling this process, the protein profiles of Smad4 mutant and control epidermal and HF keratinocytes were compared using 2‐D difference gel electrophoresis (2‐D DIGE) proteomic analysis. Eighty‐six differentially expressed protein spots were identified by MALDI‐TOF/TOF MS or ESI‐MS/MS as 72 proteins, of which 29 proteins were found to be changed during the anagen‐catagen transition of HFs in Smad4 mutants compared with the controls. The differentially expressed proteins represent a wide spectrum of functional classes such as keratin, the cytoskeleton, cellular growth and differentiation, ion combination and transfer, protein enzymes. Notably, we found that the 14‐3‐3σ protein together with the 14‐3‐3ζ and 14‐3‐3β proteins were significantly down‐regulated only in wild‐type keratinocytes but not in Smad4 mutant keratinocytes during the catagen phase, suggesting that increased expression of 14‐3‐3 proteins might contribute to the blockade of catagen initiation in Smad4 deficient HFs.