Brandon, N. | bioRxiv Science

bioRxiv2020

KCC2 is required for the survival of mature neurons but not for their development

The K+/Cl- co-transporter KCC2 (SLC12A5) allows mature neurons in the CNS to maintain low intracellular Cl- levels that are critical in mediating fast hyperpolarizing synaptic inhibition via type A {gamma}-aminobutyric acid receptors GABAARs. In accordance with this, compromised KCC2 activity results in seizures but whether such deficits directly contribute to the subsequent changes in neuronal viability that lead to epileptogenesis, remains to be assessed. Canonical hyperpolarizing GABAAR currents develop postnatally which reflect a progressive increase in KCC2 expression levels and activity. To investigate the role that KCC2 plays in regulating neuronal viability and architecture we have conditionally ablated KCC2 expression in developing and mature neurons. Decreasing KCC2 expression resulted in the rapid activation of the extrinsic apoptotic pathway, in mature hippocampal neurons. Intriguingly, direct pharmacological inhibition of KCC2 in mature neurons resulted in the rapid activation of the extrinsic apoptotic pathway. In contrast, ablating KCC2 expression in immature neurons had no discernable effects on their subsequent development, arborization or dendritic structure. However ablating KCC2 expression in immature neurons was sufficient to prevent the subsequent postnatal development of hyperpolarizing GABAAR currents. Collectively, our results demonstrate that KCC2 plays a critical role in neuronal survival by limiting apoptosis, and mature neurons are highly sensitive to loss of KCC2 function. In contrast KCC2 appears to play a minimal role in mediating neuronal development or architecture.

neuroscience↗

bioRxiv2018

Inactive USP14 and inactive UCHL5 cause accumulation of distinct ubiquitinated proteins in mammalian cells

USP14 is a cysteine-protease deubiquitinase associated with the proteasome and plays important catalytic and allosteric roles in proteasomal degradation. USP14 inhibition has been considered a therapeutic strategy for accelerating degradation of aggregation-prone proteins in neurodegenerative diseases and for inhibiting proteasome function to induce apoptotic cell death in cancers. Here we studied the effects of USP14 inhibition in mammalian cells using small molecule inhibitors and an inactive USP14 mutant C114A. Neither the inhibitors nor USP14 C114A changed the level of TDP-43, tau or -synuclein in HEK293T cells. However, USP14 C114A led to an accumulation of ubiquitinated proteins, which were isolated by ubiquitin immunoprecipitation and identified by mass spectrometry. Among these proteins we confirmed that ubiquitinated {beta}-catenin was accumulated in the cells expressing USP14 C114A with biochemistry and molecular biology experiments. The proteasome binding of USP14 C114A is required for its effect on ubiquitinated proteins. UCHL5 is the other cysteine-protease deubiquitinase associated with the proteasome. Interestingly, the inactive mutant of UCHL5 C88A also caused an accumulation of ubiquitinated proteins in HEK293T cells but did not affect {beta}-catenin. Using ubiquitin immunoprecipitation and mass spectrometry, we identified the accumulated ubiquitinated proteins in UCHL5 C88A expressing cells which are mostly distinct from those accumulated in USP14 C114A expressing cells. Among the identified proteins are well established proteasome substrates and proteasome subunits. Together our data suggest that USP14 and UCHL5 can deubiquitinate distinct substrates at the proteasome and regulate the ubiquitination of the proteasome itself which is tightly linked to its function.

molecular biology↗