Accumulation of ubiquitin-conjugated cytokeratin fragments in tumor cells

Novel K6-K14 keratin fusion enhances cancer stemness and aggressiveness in oral squamous cell carcinoma

Keratin intermediate filament (IF) is one component of cellular architectures, which provides necessary mechanical support to conquer environmental stresses. Recent findings reveal its involvement in mechano-transduction and the associated stem cell reprogramming, suggesting the possible roles in cancer development. Here, we report t(12;17)(q13.13;q21.2) chromosomal rearrangement as the most common fusion event in OSCC, resulting in a variety of inter-keratin fusions. Junction site mapping verified 9 in-frame K6-K14 variants, three of which were correlated with lymph node invasion, late tumor stages (T3/T4) and shorter disease-free survival times. When expressed in OSCC cells, those fusion variants disturbed wild-type K14 organization through direct interaction or aggregate formation, leading to perinuclear structure loss and nuclear deformation. Protein array analyses showed the ability of K6-K14 variant 7 (K6-K14/V7) to upregulate TGF-β and G-CSF signaling, which contributed to cell stemness, drug tolerance, and cell aggressiveness. Notably, K6-K14/V7-expressing cells easily adapted to a soft 3-D culture condition in vitro and formed larger, less differentiated tumors in vivo. In addition to the anti-mechanical-stress activity, our data uncover oncogenic functionality of novel keratin filaments caused by gene fusions during OSCC development.

PADI4 rs2240337 G>A polymorphism is associated with susceptibility of esophageal squamous cell carcinoma in a Chinese population

Background

Esophageal cancer (EC) remains one of the major causes of cancer incidence and mortality worldwide. Genetic factors, such as single nucleotide polymorphisms (SNPs), may contribute to the carcinogenesis of EC.

Methods

We conducted a hospital based case-control study to evaluate the genetic susceptibility of SNPs on the development of EC. A total of 629 esophageal squamous cell carcinoma (ESCC) cases and 686 controls were enrolled for this study. Seven PADI4 SNPs were determined by ligation detection reaction method.

Results

Our findings suggested that the PADI4 rs2240337 GA/AA variants were significantly associated with decreased risk of ESCC. Haplotype PADI4 A_rs2477137C_rs1886302G_rs11203366G_rs16825533G_rs2240337A_rs1635564A_rs1635562 and C_rs2477137T_rs1886302G_rs11203366A_rs1635564G_rs2240337C_rs1635564T_rs1635562 polymorphism was correlated with decreased susceptibility to ESCC, while C_rs2477137T_rs1886302A_rs11203366A_rs1635564G_rs2240337A_rs1635564A_rs1635562 was correlated with increased susceptibility of ESCC. Stratification analyses demonstrated that smoking significantly increased ESCC risk in PADI4 rs11203366 AG/AA, rs1886302 CC/CT, rs1635562 AT, rs1635564 CA and rs2477137 AC genotype. Alcohol drinking increased ESCC risk in PADI4 rs11203366 AG, rs1635562 AT, rs1635564 CA, rs2477137 AC, rs1886302 CT genotype. In younger cohort (<63 years), rs11203366 AA genotype was associated with increased risk of ESCC. PADI4 rs1886302 CC variant was associated with ESCC susceptibility in female cohort.

Conclusions

Our study suggested that PADI4 rs2240337 G>A polymorphism may be correlated with individual susceptibility to ESCC. PADI4 rs11203366, rs1886302, rs1635562, rs1635564 and rs2477137 polymorphisms were implicated with altered susceptibility of ESCC based on sex, age, smoking status and alcohol consumption. However, larger studies among different ethnic populations and further experiments using genetically mutated cells or animals are warranted to verify our conclusion.

Triple negative breast cancer: a multi-omics network discovery strategy for candidate targets and driving pathways

Triple negative breast cancer (TNBC) represents approximately 15% of breast cancers and is characterized by lack of expression of both estrogen receptor (ER) and progesterone receptor (PR), together with absence of human epidermal growth factor 2 (HER2). TNBC has attracted considerable attention due to its aggressiveness such as large tumor size, high proliferation rate, and metastasis. The absence of clinically efficient molecular targets is of great concern in treatment of patients with TNBC. In light of the complexity of TNBC, we applied a systematic and integrative transcriptomics and interactomics approach utilizing transcriptional regulatory and protein-protein interaction networks to discover putative transcriptional control mechanisms of TNBC. To this end, we identified TNBC-driven molecular pathways such as the Janus kinase-signal transducers, and activators of transcription (JAK-STAT) and tumor necrosis factor (TNF) signaling pathways. The multi-omics molecular target and biomarker discovery approach presented here can offer ways forward on novel diagnostics and potentially help to design personalized therapeutics for TNBC in the future.

The hypoxic tumor microenvironment regulates invasion of aggressive oral carcinoma cells

Invasion is an important hallmark of cancer involving interactions between the tumor microenvironment and the cancer cells. Hypoxia, low oxygen level, is related to increased invasion and metastasis in many cancers. The aim was to elucidate the effect of hypoxia on invasion of oral squamous cell carcinoma cells (OSCCs), and the applicability of a novel 3-dimentional myoma organotypic invasion model in hypoxia experiments. OSCC cell lines (primary oral carcinoma derived cells UT-SCC-43A, recurrent oral carcinoma cells UT-SCC-43B and aggressive tongue carcinoma cells HSC-3) were studied for their migration and invasion capabilities under normoxia, hypoxia, and in the presence a hypoxia-mimicker cobalt chloride. As expected, the recurrent UT-SCC-43B cells were significantly more aggressive than the primary tumor derived cells. In contrast to tongue carcinoma HSC-3 cells, they only mildly responded to hypoxia in the migration or invasion assays, indicating a cell line specific response of hypoxia on the invasive potential. The modification of the organotypic human tissue-derived matrix via the removal of various yet unidentified soluble factors by rinsing the tissue resulting in stripped matrix substantially changed the invasion pattern of HSC-3 cells and the outcomes of hypoxic treatments. Only in the stripped tissue hypoxia significantly increased invasion, whereas in native intact tissue the induced invasion was not observed. This demonstrates the importance of the soluble factors to the invasion pattern and to the hypoxia response. A metastasis and poor prognosis marker, hypoxia-regulated lysyl oxidase (LOX), was present in the myoma tissue, but could be removed by rinsing. The inhibition of LOX resulted in a decrease in invasion area, but only very mildly in invasion depth. Thus, it may have a role in the modulation of the invasion pattern. Another hypoxia-related poor prognosis marker carbonic anhydrase 9 (CAIX) was induced in HSC-3 cells both by the hypoxic exposure and interestingly in invading HSC-3 cells inside the tissue even in normoxic conditions. In conclusion, this suggests that the intact myoma organotypic model offers optimally hypoxic surroundings, thus being an excellent human tumor microenvironment mimicker.

O-GlcNAcylation determines the solubility, filament organization, and stability of keratins 8 and 18

Keratins 8 and 18 (K8/18) are intermediate filament proteins expressed specifically in simple epithelial tissues. Dynamic equilibrium of these phosphoglycoproteins in the soluble and filament pool is an important determinant of their cellular functions, and it is known to be regulated by site-specific phosphorylation. However, little is known about the role of dynamic O-GlcNAcylation on this keratin pair. Here, by comparing immortalized (Chang) and transformed hepatocyte (HepG2) cell lines, we have demonstrated that O-GlcNAcylation of K8/18 exhibits a positive correlation with their solubility (Nonidet P-40 extractability). Heat stress, which increases K8/18 solubility, resulted in a simultaneous increase in O-GlcNAc on these proteins. Conversely, increasing O-GlcNAc levels were associated with a concurrent increase in their solubility. This was also associated with a notable decrease in total cellular levels of K8/18. Unaltered levels of transcripts and the reduced half-life of K8 and K18 indicated their decreased stability on increasing O-GlcNAcylation. On the contrary, the K18 glycosylation mutant (K18 S29A/S30A/S48A) was notably more stable than the wild type K18 in Chang cells. The K18-O-GlcNAc mutant accumulated as aggregates upon stable expression, which possibly altered endogenous filament architecture. These results strongly indicate the involvement of O-GlcNAc on K8/18 in regulating their solubility and stability, which may have a bearing on the functions of these keratins.

Increased PADI4 expression in blood and tissues of patients with malignant tumors

Background

Peptidylarginine deiminase type 4 (PAD4/PADI4) post-translationally converts peptidylarginine to citrulline. Recent studies suggest that PADI4 represses expression of p53-regulated genes via citrullination of histones at gene promoters.

Methods

Expression of PADI4 was investigated in various tumors and non-tumor tissues (n = 1673) as well as in A549, SKOV3 and U937 tumor cell lines by immunohistochemistry, real-time PCR, and western blot. Levels of PADI4 and citrullinated antithrombin (cAT) were investigated in the blood of patients with various tumors by ELISA (n = 1121).

Results

Immunohistochemistry detected significant PADI4 expression in various malignancies including breast carcinomas, lung adenocarcinomas, hepatocellular carcinomas, esophageal squamous cancer cells, colorectal adenocarcinomas, renal cancer cells, ovarian adenocarcinomas, endometrial carcinomas, uterine adenocarcinomas, bladder carcinomas, chondromas, as well as other metastatic carcinomas. However, PADI4 expression was not observed in benign leiomyomas of stomach, uterine myomas, endometrial hyperplasias, cervical polyps, teratomas, hydatidiform moles, trophoblastic cell hyperplasias, hyroid adenomas, hemangiomas, lymph hyperplasias, schwannomas, neurofibromas, lipomas, and cavernous hemangiomas of the liver. Additionally, PADI4 expression was not detected in non-tumor tissues including cholecystitis, cervicitis and synovitis of osteoarthritis, except in certain acutely inflamed tissues such as in gastritis and appendicitis. Quantitative PCR and western blot analysis showed higher PADI4 expression in gastric adenocarcinomas, lung adenocarcinomas, hepatocellular carcinomas, esophageal squamous cell cancers and breast cancers (n = 5 for each disease) than in the surrounding healthy tissues. Furthermore, western blot analysis detected PADI4 expression in cultured tumor cell lines. ELISA detected increased PADI4 and cAT levels in the blood of patients with various malignant tumors compared to those in patients with chronic inflammation and benign tumors. This was consistent with immunohistochemical results. Additionally, PADI4 and cAT levels were significantly associated with higher levels of known tumor markers.

Conclusion

Our results suggest that PADI4 expression is increased in the blood and tissues of many malignant tumors, a finding useful for further understanding of tumorigenesis.

Role of autophagy in cancer: management of metabolic stress

Human breast, ovarian, and prostate tumors display allelic loss of the essential autophagy gene beclin1 with high frequency, and an increase in the incidence of tumor formation is observed in beclin1(+/-) mutant mice. These findings suggest a role for beclin1 and autophagy in tumor suppression; however, the mechanism by which this occurs has been unclear. Autophagy is a bulk degradation process whereby organelles and cytoplasm are engulfed and targeted to lysosomes for proteolysis,(1,2) There is evidence that autophagy sustains cell survival during nutrient deprivation through catabolism, but also that autophagy is a means of achieving cell death when executed to completion. If or how either of these diametrically opposing functions proposed for autophagy may be related to tumor suppression is unknown. We found that metabolic stress is a potent trigger of apoptotic cell death, defects in which enable long-term survival that is dependent on autophagy both in vitro and in tumors in vivo.(3) These findings raise the conundrum whereby inactivation of a survival pathway (autophagy) promotes tumorigenesis. Interestingly, when cells with defects in apoptosis are denied autophagy, this creates the inability to tolerate metabolic stress, reduces cellular fitness, and activates a necrotic pathway to cell death. This necrosis in tumors is associated with inflammation and enhancement of tumor growth, due to the survival of a small population of surviving, but injured, cells in a microenvironment that favors oncogenesis. Thus, by sustaining metabolism through autophagy during periods of metabolic stress, cells can limit energy depletion, cellular damage, and cell death by necrosis, which may explain how autophagy can prevent cancer, and how loss of a survival function can be tumorigenic.

Mallory body forming cells express the preneoplastic hepatocyte phenotype

The livers of mice fed diethyl 1,4-dihydro-2,4,6,-trimethyl-3,5-pyridinedicarboxylate (DDC) for 10 weeks formed Mallory bodies (MBs) in clusters of hepatocytes. Mice withdrawn from DDC for 9 months developed liver tumors. In the present study, the phenotype of the hepatocytes that formed MBs and tumors was characterized. Immunoperoxidase and immunofluorescent stains were done on the DDC-treated mouse livers, as well as mouse liver tumors and a human hepatocellular carcinoma that formed MBs. Antibodies to markers of hepatocellular neoplasms such as alpha-fetoprotein (AFP), ubiquitin B (UbB) fatty acid synthase (FAS) and alpha2 macroglobulin (A2m) stained the MB forming cells positive. Quantitative real-time RT-PCR assay was used to measure AFP, UbB, FAS and GCP-3 A2m mRNA levels in the livers of DDC fed mice and the DDC-induced mouse liver tumors. The FAS, UbB, GPC-3 and AFP mRNA levels were significantly increased in the MB forming liver cells. The in vitro model of MB formation was used to correlate MB formation with gene and protein expression. Primary cultures of DDC-primed hepatocytes were compared with the controls. A2m and UbB expression increased in the primary cultures of DDC-primed hepatocytes when MBs formed. Thus, the tumor markers used to identify hepatocellular carcinoma were upregulated in cells forming MBs in vivo and in vitro, suggesting that MB forming cells express preneoplastic phenotypic features.