A novel link between calcineurin, amino acid permease, and protein kinase A in virulence in Mucor - Summary Mucormycosis, which is caused by Mucorales fungi, is a life-threatening condition that poses a challenge to immunocompromised patients. As the susceptible cohort increases, the incidence of mucormycosis is rising. Mucormycosis has an unacceptably high mortality rate of more than 90% in disseminated infections and 50% overall in all cases. To make matters even worse, a number of reports concern the high level of intrinsic antifungal resistance in Mucorales. Therefore, there is an urgent need for the development of new antifungals to overcome lethal fungal infections. One very well-known virulence factor in fungi is calcineurin, a serine/threonine phosphatase, which is required for the invasive hyphal growth in the model Mucorales Mucor circinelloides (denote Mucor). This attribute of the phosphatase makes a highly attractive target of antifungal drugs. However, calcineurin is highly conserved in fungi and humans, which in practical terms has translated into our inability (despite major efforts by multiple groups of investigators over the years) to directly use pharmacological inhibition of calcineurin as an antifungal strategy. Fungal specific downstream of calcineurin that is absent in mammalian cells will potentially solve the conundrum and open a brand-new avenue for the development of novel antifungal drugs. During preliminary studies, we discovered that, in Mucor, 1) mutations in an amino acid permease gene results in resistance to calcineurin inhibitors such as FK506, 2) the resistance is caused by an elevated activity of protein kinase A (PKA), and 3) the amino acid permease positively regulates the activity of PKA. These observations have never been reported in any fungal systems and will lead a completely different direction to study calcineurin as a target for drugs. Based on this observation, our hypothesis in this proposal is that the resistance mechanism to calcineurin inhibitors via the genetic link between calcineurin, amino acid permease, and PKA is conserved in pan-fungal systems. Three specific aims include identification of a key transcription factor(s) regulated by calcineurin in the regulation of the amino acid permease BycA expression (Aim 1), elucidation of the roles of BycA in virulence (Aim 2), and demonstration of the link between BycA and PKA (Aim 3).
