KlMID1 a relevant key player between ER homeostasis and mitochondrial dysfunction in Kluyveromyces lactis.

The interplay between calcium metabolism and glycosylation in yeast is largely unknown. In order to clarify this relationship, the effect of the mutation in KlOCH1 gene, coding for the Golgi α-1,6-mannosyltransferase, on the calcium homeostasis was studied in the Kluyveromyces lactis yeast. In particular, the role of KlMID1 gene, encoding one of the components of the plasma membrane calcium channel (Cch1-Mid1), was investigated. Almost complete suppression of the phenotypes occurring in the mutant strain, ranging from oxidative stress to cell wall alteration, was observed by increased dosage of KlMID1. In addition, this N-glycosylation mutant showed increased calcium accumulation and decreased transcription of KlMID1 and KlCCH1. Moreover, the calcium alterations included the increased expressional profile of the KlPMC1 gene, coding for the vacuolar calcium ion pump. Furthermore, perturbation of endoplasmic reticulum homeostasis was observed in the Kloch1-1 cells. Similarly, down modulation of calcium signalling genes as well as altered mitochondria functionality were induced in the wild type cells after treatment with dithiothreitol (DTT). However, no mitochondrial alteration occurred in the treated cells when KlMID1 was overexpressed.Our results suggest that ER stress taking place in Kloch1-1 cells appears to be the primary cause for KlMID1 down-modulation and its resulting effects on the expression of calcium homeostasis genes.