Role of HxkC, a mitochondrial hexokinase-like protein, in fungal programmed cell death

Apoptosis is a form of programmed cell death (PCD) that occurs during animal development and is also triggered by a variety of signals including nutrient or oxidative stress, hypoxia, DNA damage, viral infection and oncogenic transformation. Though apoptotic-like PCD also occurs in plants and fungi, genes encoding several of the key players in mammalian apoptosis (p53 and BH-domain proteins) have not been identified in these kingdoms. In this report we investigated whether HxkC, a mitochondrial hexokinase-like protein, and XprG, a putative p53-like transcription factor similar to Ndt80, play a role in programmed cell death in the filamentous fungus 'Aspergillus nidulans'. We show that a mutant lacking HxkC is more sensitive to oxidative stress. Autolysis, a form of fungal programmed cell death triggered by carbon starvation, is accelerated in the hxkC∆1 mutant but not the hxkC∆1 xprG∆1 double mutant. In the absence of nutrient stress, the hxkC∆1 mutant displays XprG-dependent DNA fragmentation typical of apoptosis and elevated levels of intracellular protease. HxkC and XprG are required for catabolism of N-acetylglucosamine, as in 'Trichoderma reesei'. We show that XprG is present in the nucleus. We conclude that, like mammalian mitochondrial hexokinase, HxkC has anti-apoptotic activity and the XprG transcription factor has a pro-apoptotic role in filamentous fungi.