The Kv1.3 potassium channel is localized to the cis‐Golgi and Kv1.6 is localized to the endoplasmic reticulum in rat astrocytes

Abstract

The functions of voltage‐gated potassium (Kv) channels in neurons have been well defined, whereas their roles in glial cells are not fully understood. Kv1.1, Kv1.3 and Kv1.6 are endogenously expressed in C6 astrocytoma cells, but their trafficking and subcellular localization have not been well studied. In C6 cells, Kv1.1 was localized to the cell surface, Kv1.3 was predominantly localized in the cis‐Golgi, and Kv1.6 was enriched in the endoplasmic reticulum. Disruption of the Golgi stacks with brefeldin A treatment redirected Kv1.3 to the endoplasmic reticulum, further confirming that Kv1.3 was localized in the Golgi. Denaturing and reducing immunoblot analysis identified an expected Kv1.3 monomer and an unexpected Kv1.3 dimer/aggregate. These two forms had different protein half‐lives: that of the monomer form T1/2 was 5.1 h, whereas the dimer/aggregate form was stable over the 8‐h measurement period. The Kv1.3 dimer/aggregate form on immunoblots appeared to be correlated with its Golgi retention, based on examination with several cell types that expressed Kv1.3. Glycosidase treatment showed that Kv1.3 contained complex‐type N‐glycans terminated with sialic acids, suggesting that Kv1.3 had traveled to the trans‐Golgi network for sialylation before it was recycled to the cis‐Golgi for retention. Inhibition of N‐glycosylation did not affect Kv1.3 localization, indicating that N‐glycans did not play a role in its Golgi retention. Thus, Kv1.3 appears to be distributed to the cis‐Golgi membrane of rat astrocytes in a similar way as a Golgi resident protein, and this unusual distribution appears to be correlated with its SDS/2‐mercaptoethanol‐resistant dimer/aggregate forms on immunoblots.

Targeting Kv1.3 channels to reduce white matter pathology after traumatic brain injury

“…This intracellular shift is consistent with the reported movement of Kv1.3 protein within CNS microglia exposed to direct current stimulation during proliferation in vitro (Kotecha and Schlichter, 1999). As predicted from the literature (Zhu et al, 2014), we also found that callosal astrocytes express Kv1.3, albeit at a lower level than microglia (Fig. 10B).…”

“…Kv1.3 protein mobilization during microglial activation not only demonstrates the functional relevance of Kv1.3 channels, but also suggests that their susceptibility to selective channel blockers could alter microglial reactivity after white matter injury. In this context, we also probed for Kv1.3 by WB in callosal mixed glial cultures ( data not shown ), where we observed a single 55kD Kv1.3 species, smaller than the predicted 68-70 kD monomer or the 160 kD dimerized channel protein (Kotecha 1999; Fadool 1997; Zhu, 2014). Since higher kD tyrosine phosphorylated forms of the channel show functional suppression (Colley and Fadool, 2004), we speculate that the 55kD in callosal glial cultures may represent an active, less phosphorylated Kv1.3 form.…”

“…Kv1.3 is expressed in numerous CNS cell types including not only microglia (Khanna et al, 2001; Panasch et al, 2006; Rangaraju et al, 2015) but also astrocytes (Zhu et al, 2014), oligodendrocytes (Chittajallu et al, 2002), olfactory bulb neurons (Fadool et al, 2004), Purkinje cells (Mckay et al, 2005), and cortical interneurons (Duque et al, 2013). Kv1.3 signaling mechanism has been characterized in most detail for T lymphocytes (reviewed by Cahalan and Chandy, 2009).…”

Targeting the Potassium Channel Kv1.3 Kills Glioblastoma Cells

“…expression of Kv1.3 in mitochondrial and plasma membranes, had already been found in breast cancer MCF-7, prostate cancer PC3, osteosarcoma SAOS-2, melanoma B16F10, Jurkat T cell lymphoma [22,26,27] and pancreas carcinoma [28]. In addition, recent data indicate the presence of Kv1.3 also in cis-Golgi [29] and in the nuclear membrane [30], which is also consistent with the present studies. The function of the cis-Golgi-located channels is unknown, while nuclear Kv1.3 has been suggested to impact on transcription factor activation via regulation of the nuclear membrane potential.…”

Tumor-reducing effect of the clinically used drug clofazimine in a SCID mouse model of pancreatic ductal adenocarcinoma

“…Kv1.3 was located to the cis-Golgi membranes as well [29] and, recently, to the nuclear membrane [30] where it seems to be involved in regulation of transcription. Expression of the channel in the IMM seems to correlate with that in the PM (e.g.…”