Keratins provide virus-dependent protection or predisposition to injury in coxsackievirus-induced pancreatitis

Abstract

Keratins 8 and 18 (K8/K18) are the two major intermediate filament proteins in hepatocytes and pancreatic acinar cells. Acinar cell keratins are organized as cytoplasmic and apicolateral filaments. An important role of hepatocyte K8/K18 is to maintain cellular integrity, while this cytoprotective function of K8/K18 is not evident in the pancreas since keratin-deficient mice cope well with pancreatitis models. To further study the roles of keratins in the exocrine pancreas, we used coxsackievirus B4-models, CVB4-V and CVB4-P, to induce severe acute/chronic pancreatitis and acute pancreatitis, respectively, in K8-null (which lack acinar keratins) and K18-null (which lack cytoplasmic keratins) mice. Despite similar virus titers in all mice, CVB4-V resulted in 40% mortality of the K8-null mice 14 days post-infection compared to no lethality of WT and K18-null mice. In contrast, K8-null mice were far less susceptible to CVB4-P-induced damage as determined by histology and serology analysis, and they recover faster than WT and K18-null mice. After CVB4 virus infection, keratins aggregated during acinar degranulation, and K8/K18 site-specific phosphorylation was observed during degranulation and recovery. Hence, keratins significantly affect CVB4 virulence, positively or negatively, depending on the virus subtype and keratin makeup, in a virus replication-independent manner.

Intermediate filaments take the heat as stress proteins

“…More pointedly, K8, K18 or K19 mutations are silent under normal circumstances yet predispose to liver injury and apoptosis (e.g., mediated by toxins), or to mechanical fragility of hepatocytes (upon isolation by liver perfusion in keratin-mutant or keratin-deficient mice) depending on the location of the mutation [11]. However, there are a few exceptions, including K8-null mice that are protected from coxsackievirus-induced pancreatitis [24], and double-null GFAP/vimentin mice which develop attenuated reactive gliosis after neurotrauma [25]. In summary, there is compelling evidence for an important role for IFs in the stress response in a context-dependent manner.…”

Keratin 6a reorganization for ubiquitin–proteasomal processing is a direct antimicrobial response

“…Accumulating evidence reveals that keratins regulate diverse cellular functions, including gene and protein expression ( Kim et al, 2006 ; Hobbs et al, 2015 ), subcellular targeting of protein and organelles ( Petrosyan et al, 2015 ), and cell growth, survival, and differentiation ( Ku et al, 2010 ; Fu et al, 2014 ; Petrosyan et al, 2015 ; Hobbs et al, 2016 ). PTMs are crucial to the functions of keratins ( Sawant and Leube, 2017 ), and our data reveal new functional significance of keratin phosphorylation in innate immunity ( Geisler and Leube, 2016 ), which may provide exciting insights into the association of K8/18 hyperphosphorylation and network remodeling with virus infection in hepatocytes, pancreatic acinar cells, and intestinal epithelial cells ( Liao et al, 1995 ; Toivola et al, 2004 , 2009 ). Similar to K8, K17, and K18 phosphorylation ( Liao and Omary, 1996 ; Ku et al, 2002 ; Kim et al, 2006 ), K6a phosphorylation might enhance its interaction with the cytoplasmic adapter and scaffolding 14-3-3 proteins.…”

Keratin 8 modulates β-cell stress responses and normoglycaemia

“…2/2 endocrine cell protection relates to similar cytoprotective mechanisms to those that have been described for the exocrine pancreas, which in K8 2/2 mice is highly resistant to injury in several non-chronic experimental pancreatitis models (Toivola et al, 2009;Toivola et al, 2000a). This exocrine cytoprotection is related to the dramatic upregulation of the injury-response protein regeneration protein 2 (REG2) in the K8 2/2 mouse acinar cells under basal conditions (Zhong et al, 2007).…”

“…This is exemplified by the remarkable stress tolerance of the exocrine pancreas to K8 or K18 mutation or knockout. Despite K8 and K18 being the major keratins in the liver and exocrine pancreas, keratin absence does not increase susceptibility to exocrine-specific pancreatitis induced by caerulein, choline-deficient diet (Toivola et al, 2000a) or acute coxsackievirus-induced pancreatits (Toivola et al, 2009).…”