Trichophyton rubrum DNA strain switching increases in patients with onychomycosis failing antifungal treatments.

BACKGROUND: The dermatophyte Trichophyton rubrum is responsible for approximately 80% of onychomycosis cases. Genetic strain typing was developed to help elucidate its epidemiology and pathogenicity. OBJECTIVES: To determine T. rubrum DNA strain types in North American patients with onychomycosis and to track the patients before and after their course of treatments. METHODS: T. rubrum DNA strain types were determined by restriction fragment length polymorphisms in ribosomal DNA and Southern blotting from toenails that were cultured from 50 North American patients with onychomycosis prior to treatment. Some of the patients were subsequently typed from oral terbinafine (n = 6), laser (n = 9) or placebo (n = 8) treatment groups. Three European DNA strains were obtained for comparison. DNA strains from the terbinafine group were tested for in vitro susceptibility to terbinafine. RESULTS: Six DNA strain types (A-F) accounted for 94% of T. rubrum DNA strains and corresponded to European isolates. Three DNA strains (6%) novel to North America were detected. DNA strain type switching occurred in all treatment groups: terbinafine (83%), laser (56%) and placebo (25%). Most of the switches (50%) observed in the terbinafine group coincided with mycological cures followed by relapse. Patients treated with laser therapy or placebo exhibited no intermittent cures. DNA strains from the terbinafine group were all susceptible to terbinafine in vitro. CONCLUSIONS: Nine T. rubrum DNA strains were identified in a North American population: three novel and six predominant to a European population. Although DNA strain type switching in onychomycosis is a natural phenomenon, with presence in the placebo group, increases following the course of failed onychomycosis treatment suggest an antifungal-induced response.

Phosphorylation by p38 MAP kinase is required for E2F1 degradation and keratinocyte differentiation.

The transcription factor E2F1 plays key roles in skin homeostasis, and is essential for normal keratinocyte proliferation and epidermal regeneration after injury. We have previously established that, in differentiating keratinocytes, E2F1 activity is controlled by nuclear export and subsequent degradation. These events are triggered by differentiation-induced stimulation of protein kinase C and p38 mitogen-activated protein kinase (MAPK). However, the mechanisms that induce E2F1 export from the nucleus and the role of p38 MAPK in this process are poorly understood. We now describe a novel regulatory pathway for E2F1, which involves phosphorylation by p38. We demonstrate that E2F1 forms complexes with active p38 through regions that exclude the N-terminus of this transcription factor, and that p38 activity is a major contributor to the phosphorylation status of E2F1 in keratinocytes. Using in vitro kinase assays, we identified Ser403 and Thr433 as the residues phosphorylated by p38. The biological significance of these observations is underscored by the inability of E2F1 mutants lacking one or both of these residues to be exported from the nucleus and degraded when keratinocytes receive differentiation stimuli, which results in impaired keratinocyte maturation.