P4.39 LOCALIZATION OF MYC/MAD1 PROTEIN IN THE HAIR FOLLICLE DURING HAIR CYCLE

Norimitsu Saito, Yuko Hamada, Kensei Katsuoka

Department of Dermatology, Kitasato University School of Medicine, Sagamihara, Japan.

Objectives: Precise molecular mechanisms associated with transient growth/differentiation of follicular keratinocytes have not been fully elucidated in the hair cycle. Recent observations have suggested that proto-oncogene c-myc plays a pivotal role in the regulation of both apoptosis and growth in the epitherial cells. Mad1 is a Myc antagonist that functions as a transcriptional repressor. Inhibition of proliferative activity subsequent to Mad1 overexpression has been demonstrated in a variety of cell types, including keratinocytes. However, little is known about the Myc/Mad1 expression in follicular keratinocytes. To elucidate whether c-Myc/Mad1 proto-oncogenes could be involves in hair cycle, in situ expression of Myc/ Mad1 protein was investigated.

Methods: Immunohistochemical analysis was performed for the specimens taken from the plucking-induced anagen hair follicle in C3H/HeNCrj mice and human anagen follicle. Antibodies against PCNA (Proliferating Cell Nuclear Antigen), ki67, c-Myc and Mad1 were used. The expression of c-myc/mad1 mRNA was semi-quantitated in different phases of hair cycle by RT-PCR.

Results: Immunoreactivity for ki67 was observed in the bottom portion of the inner root sheath in human anagen hair follicles. In contrast, c-Myc-positive cells were visible in Huxley’s and Henley’s layer of the inner root sheath and Mad was expressed in whole human anagen hair follicles as shown by confocal microscopy. Immunolocalization of PCNA was intensely observed both in the middle portion and the matrix of early anagen follicles in C3H mice. In the mid-anagen phase, PCNA positive cells were located only in the matrix. The expression of c-Myc mRNA was detected in the mid-anagen phase, whereas Mad1 mRNA was expressed in the early anagen phase by RT-PCR. Immunoreactivity for c-Myc-positive cells was visible in Huxley’s and Henley’s layer of the inner root sheath of mice in late anagen and catagen follicles.

Conclusions: C-Myc and Mad overexpression might be related with switching to the hair cycle. These findings suggest that c-Myc has been implicated not only in cell proliferation, but also in terminal differentiation and Mad has been implicated in cell differentiation in the hair cycle.