Novel insights into changes in biochemical properties of keratins 8 and 18 in griseofulvin-induced toxic liver injury

Revealing the Roles of Keratin 8/18-Associated Signaling Proteins Involved in the Development of Hepatocellular Carcinoma

Although hepatocellular carcinoma (HCC) is developed with various etiologies, protection of hepatocytes seems basically essential to prevent the incidence of HCC. Keratin 8 and keratin 18 (K8/K18) are cytoskeletal intermediate filament proteins that are expressed in hepatocytes. They maintain the cell shape and protect cells under stress conditions. Their protective roles in liver damage have been described in studies of mouse models, and K8/K18 mutation frequency in liver patients. Interestingly, K8/K18 bind to signaling proteins such as transcription factors and protein kinases involved in HCC development. Since K8/K18 are abundant cytoskeletal proteins, K8/K18 binding with the signaling factors can alter the availability of the factors. Herein, we discuss the potential roles of K8/K18 in HCC development.

Effects of cerulein on keratin 8 phosphorylation and perinuclear reorganization in pancreatic cancer cells: Involvement of downregulation of protein phosphatase 2A and alpha4

Toxicants can perturb cellular homeostasis by modifying phosphorylation-based signaling. In the present study, we examined the effects of cerulein, an inducer of acute pancreatitis, on keratin 8 (K8) phosphorylation. We found that cerulein dose-dependently induced K8 phosphorylation and perinuclear reorganization in PANC-1 cells, thus leading to migration and invasion. The extracellular signal-regulated kinases (ERK) inhibitor U0126 suppressed cerulein-induced phosphorylation of serine 431 and reorganization of K8. Cerulein reduced the expressions of protein phosphatase 2A (PP2A) via ubiqutination and alpha4. PP2A's involvement in K8 phosphorylation of PANC-1 cells was also confirmed by the observation that PP2A gene silencing resulted in K8 phosphorylation and migration of PANC-1 cells. Overall, these results suggest that cerulein induced phosphorylation and reorganization through ERK activation by downregulating PP2A and alpha4, leading to increased migration and invasion of PANC-1 cells. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 2090-2098, 2016.

Phosphorylation and Reorganization of Keratin Networks: Implications for Carcinogenesis and Epithelial Mesenchymal Transition

Metastasis is one of hallmarks of cancer and a major cause of cancer death. Combatting metastasis is highly challenging. To overcome these difficulties, researchers have focused on physical properties of metastatic cancer cells. Metastatic cancer cells from patients are softer than benign cancer or normal cells. Changes of viscoelasticity of cancer cells are related to the keratin network. Unexpectedly, keratin network is dynamic and regulation of keratin network is important to the metastasis of cancer. Keratin is composed of heteropolymer of type I and II. Keratin connects from the plasma membrane to nucleus. Several proteins including kinases, and protein phosphatases bind to keratin intermediate filaments. Several endogenous compounds or toxic compounds induce phosphorylation and reorganization of keratin network in cancer cells, leading to increased migration. Continuous phosphorylation of keratin results in loss of keratin, which is one of the features of epithelial mesenchymal transition (EMT). Therefore, several proteins involved in phosphorylation and reorganization of keratin also have a role in EMT. It is likely that compounds controlling phosphorylation and reorganization of keratin are potential candidates for combating EMT and metastasis.

Characterization of myeloid-specific peroxidase, keratin 8, and dual specificity phosphatase 1 as innate immune genes involved in the resistance of crucian carp (Carassius auratus gibelio) to Cyprinid herpesvirus 2 infection

Myeloid-specific peroxidase (MPO), keratin 8 (KRT-8), and dual specificity phosphatase 1 (DUSP-1) are believed to play essential roles in innate immunity. Through suppression subtractive hybridization (SSH) analysis, we previously identified MPO, KRT-8, and DUSP-1 as the three genes that were the most significantly upregulated in crucian carp (Carassius auratus gibelio) that survived Cyprinid herpesvirus 2 (CyHV-2) infection. Here, we have further characterized these three genes and their response to pathogen challenge. The open reading frames (ORF) of MPO, KRT-8, and DUSP-1 were cloned by RACE technique and sequenced. The full-length cDNAs of the three genes contained ORFs of 2289, 1575 and 1083 bp respectively. The polypeptides from each ORF were projected to contain 762 (MPO), 524 (KRT-8), and 360 (DUSP-1) amino acids. Phylogenetic analysis showed that the three genes were most closely related to zebrafish. We found that MPO, KRT-8, and DUSP-1 were expressed at low levels in all of the tissues examined in healthy crucian carp. Quantitative real-time RT-PCR analysis indicated that MPO, KRT-8, and DUSP-1 mRNA expression was significantly upregulated within 72 h of CyHV-2 infection compared to mock infected controls. Maximum expression of MPO was detected at 24 hpi (2.71-fold, P < 0.05). While, 12 hpi (3.80-fold, P < 0.01) and 6 hpi (8.70-fold, P < 0.01) were the highest expression time points for KRT-8 and DUSP-1, respectively. In contrast, after Aeromonas hydrophila challenge, the transcripts of these three genes remained unchanged or slightly down-regulated. For the fish survived from viral infection, expression levels of MPO and KRT-8 were 2.72 fold and 2.47 fold higher than those of fish died from acute infection, and similar level of DUSP-1 was observed in samples of survived fish. These data suggested MPO, KRT-8 and DUSP-1 might be involved in the antiviral, but not antibacterial innate immune response in crucian carp. These findings also support the use of MPO and KRT-8 as immunological markers for a response to viral infection in crucian carp.

Cytoskeleton in motion: the dynamics of keratin intermediate filaments in epithelia

Epithelia are exposed to multiple forms of stress. Keratin intermediate filaments are abundant in epithelia and form cytoskeletal networks that contribute to cell type–specific functions, such as adhesion, migration, and metabolism. A perpetual keratin filament turnover cycle supports these functions. This multistep process keeps the cytoskeleton in motion, facilitating rapid and protein biosynthesis–independent network remodeling while maintaining an intact network. The current challenge is to unravel the molecular mechanisms underlying the regulation of the keratin cycle in relation to actin and microtubule networks and in the context of epithelial tissue function.

Cytokeratins in hepatitis

Experimental and clinical evidence suggests that cytokeratins (CK), among other physiological functions, are expressed in hepatocytes and can be released in the bloodstream after acute or chronic inflammatory liver injury. Interest in CK in viral and nonviral hepatitis has been rapidly increasing during the last years, especially as they have been proposed as circulating biomarkers of hepatocyte necrosis and apoptosis. In the present review, we sought to summarize and discuss the alterations in circulating CK levels in different form viral and nonviral hepatitis, as well as their potential relation with liver histology. Understanding the mechanisms of hepatitis impact on CK and vice versa is a promising area of research that will positively enhance our understanding of the complexity of acute and chronic inflammatory liver injury.

Cell death and nonalcoholic steatohepatitis: where is ballooning relevant?

Nonalcoholic fatty liver disease (NAFLD) is the most common form of liver disease in the Western world. Progression to more aggressive forms of liver injury, such as nonalcoholic steatohepatitis (NASH) and cirrhosis, occurs in less than a third of affected subjects. Human data and both in vivo and in vitro models demonstrate that cell death, particularly apoptosis, is increased in NAFLD and NASH patients, suggesting that it is crucial in disease progression. Indeed, fatty acids - more specifically, saturated fatty acids - strongly induce hepatocyte apoptosis. In addition, hepatic steatosis renders hepatocytes more susceptible to apoptotic injury. Ballooned hepatocytes and Mallory-Denk bodies are important hallmarks of NASH and correlate with disease progression. There are complex correlations between ballooning, Mallory-Denk bodies and apoptosis through keratin metabolism and depletion, as well as through the endoplasmic reticulum stress response. Whether apoptosis may promote hepatocellular ballooning, or vice versa, will be discussed in this article.