Opposite Roles Of Tgf-ß1-Responsive Tsc22d Proteins In Regulating Cerebellar Granule Neurons Differentiation And Commitment To Apoptosis

The TSC22D (Transforming Growth Factor ß1-stimulated clone 22 domain) protein family includes widely expressed members having a TSC box and a leucine zipper domain and controlling multiple biological processes. Among these members, TSC22D4 is involved in cerebellum granule neuron (CGN) differentiation and commitment to apoptosis. These opposite functions rely on the existence of multiple TSC22D4 forms differing in modification, subcellular localization and function. In contrast to 42 kDa and 55 kDa forms, 67 kDa and 72 kDa forms have specific posttranslational modifications and subcellular localizations: the 67 kDa form is O-GlcNAcylated and unphosphorylated, whereas the 72 kDa form is O-GlcNAcylated and phoshorylated. Moreover, while the latter form is associated with chromatin, the 67 kDa form is associated with Apoptosis Inducing Factor (AIF) in mitochondria under normal cell viability conditions. However, when CGNs are committed to apoptosis the 67 kDa form is rapidly transferred from mitochondria to nuclear matrix with a kinetics similar to that of AIF transfer from mitochondria to chromatin, suggesting that the mitochondrial release of AIF and TSC22D4 is triggered by a regulatory mechanism(s) acting upon the entire AIF-TSC22D4 complex. Besides Tsc22d4, CGNs also express Tsc22d1, the first identified member of TSC22D family, which is in turn expressed with two splice variants encoding TSC22D1-1 and TSC22D1-2 proteins. While TSC22D1-2 is consistently expressed during CGN differentiation, TSC22D1-1 is highly expressed in undifferentiated CGNs and barely detected in fully differentiated CGNs. CGN apoptosis commitment triggers TSC22D1-1 translocation from the nucleus to the cytoplasm but does not modifies the nucleo/cytoplasmic distribution of TSC22D1-2. By immunoprecipitation experiments we have found that both TSC22D1-1 and TSC22D1-2 interact with TSC22D4 and that TSC22D1-1 also interacts with large conductance Ca+2-activated K+ channels (BKCa). Our findings on TSC22D4 and TSC22D1 subcellular localization/interacting protein partners depending on CGN differentiation/functional condition will be presented.