The 19S proteasome subunit Rpt5 reversibly associates with cold-stable microtubules in glial cells at low temperatures.

The ubiquitin-proteasome system (UPS) degrades intracellular proteins through the 26S proteasome. We analysed how cold stress affects the UPS in glial cells. Together with a reduction in the 20S proteolytic activity and increased levels of polyubiquitinated proteins, exposure of glial cell cultures to cold induces a partial disassembly of the 26S proteasome. In particular, we found that Rpt5, a subunit of the 19S proteasome, relocates to cold-stable microtubules, although no apparent cytoskeletal redistribution was detected for other analysed subunits of the 19S or 20S complexes. Furthermore, we demonstrate that both the expression of the microtubule-associated protein MAP6 and the post-translational acetylation of α-tubulin modulate the association of Rpt5 with microtubules. This reversible association could be related to functional preservation of the proteolytic complex during cold stress.

Ablation of arginyl-tRNA-protein transferase in oligodendrocytes impairs central nervous system myelination.

Addition of arginine (Arg) from tRNA can cause major alterations of structure and function of protein substrates. This post-translational modification, termed protein arginylation, is mediated by the enzyme arginyl-tRNA-protein transferase 1 (Ate1). Arginylation plays essential roles in a variety of cellular processes, including cell migration, apoptosis, and cytoskeletal organization. Ate1 is associated with neuronal functions such as neurogenesis and neurite growth. However, the role of Ate1 in glial development, including oligodendrocyte (OL) differentiation and myelination processes in the central nervous system, is poorly understood. The present study revealed a peak in Ate1 protein expression during myelination process in primary cultured OLs. Post-transcriptional downregulation of Ate1 reduced the number of OL processes, and branching complexity, in vitro. We conditionally ablated Ate1 from OLs in mice using 2',3'-cyclic nucleotide 3'-phosphodiesterase-Cre promoter ("Ate1-KO" mice), to assess the role of Ate1 in OL function and axonal myelination in vivo. Immunostaining for OL differentiation markers revealed a notable reduction of mature OLs in corpus callosum of 14-day-old Ate1-KO, but no changes in spinal cord, in comparison with wild-type controls. Local proliferation of OL precursor cells was elevated in corpus callosum of 21-day-old Ate1-KO, but was unchanged in spinal cord. Five-month-old Ate1-KO displayed reductions of mature OL number and myelin thickness, with alterations of motor behaviors. Our findings, taken together, demonstrate that Ate1 helps maintain proper OL differentiation and myelination in corpus callosum in vivo, and that protein arginylation plays an essential role in developmental myelination.