TREX2 is a proofreading 3 ¶-5 ¶ exonuclease that can be involved in genome maintenance; however, its biological role remains undefined. To better understand the function and physiologic relevance of TREX2, we generated mice deficient in TREX2 by targeted disruption of its unique coding exon. The knockout mice are viable and do not show relevant differences in growth, survival, lymphocyte development, or spontaneous tumor incidence compared with their wild-type counterparts over a period of up to 2 years. Also, we did not observe chromosomal instability or defects in cell proliferation and cell cycle upon loss of TREX2. We have observed that TREX2 expression is not ubiquitous, being expressed preferentially in tissues with stratified squamous epithelia, such as the skin or esophagus, and specifically in keratinocytes. Interestingly, TREX2-null mice are more susceptible to skin carcinogenesis induced by 7,12-dimethylbenz(a)anthracene (DMBA) compared with wild-type mice. This phenotype correlates with a reduction of DMBA-induced apoptosis in both the epidermis and keratinocytes of TREX2-null mice. Altogether, our results suggest a tumor suppressor role for TREX2 in skin carcinogenesis through which it contributes to keratinocyte apoptosis under conditions of genotoxic stress. [Cancer Res 2009;69(16):6676-84]

TREX2 is a 3′-DNA exonuclease specifically expressed in keratinocytes. Here, we investigated the relevance and mechanisms of TREX2 in ultraviolet (UV)-induced skin carcinogenesis. TREX2 expression was up-regulated by chronic UV exposure whereas it was de-regulated or lost in human squamous cell carcinomas (SCCs). Moreover, we identified SNPs in the TREX2 gene that were more frequent in patients with head and neck SCCs than in healthy individuals. In mice, TREX2 deficiency led to enhanced susceptibility to UVB-induced skin carcinogenesis which was preceded by aberrant DNA damage removal and degradation as well as reduced inflammation. Specifically, TREX2 loss diminished the up-regulation of IL12 and IFNγ, key cytokines related to DNA repair and antitumor immunity. In UV-treated keratinocytes, TREX2 promoted DNA repair and passage to late apoptotic stages. Notably, TREX2 was recruited to low-density nuclear chromatin and micronuclei, where it interacted with phosphorylated H2AX histone, which is a critical player in both DNA repair and cell death. Altogether, our data provide new insights in the molecular mechanisms of TREX2 activity and establish cell autonomous and non-cell autonomous functions of TREX2 in the UVB-induced skin response.

Trex2 is a keratinocyte-specific 3'-deoxyribonuclease that participates in the maintenance of skin homeostasis after DNA damage. Here, we show that this exonuclease is strongly upregulated in human psoriasis, a hyperproliferative and inflammatory skin disease. Similarly, the imiquimod (IMQ)- and Il23-induced mouse psoriasis was associated with a substantial upregulation of Trex2, which was recruited into fragmented chromatin in keratinocytes that were undergoing impaired proliferation, differentiation, and cell death, indicating an important role in DNA processing. Using Trex2 knockout mice, we have found that Trex2 deficiency attenuated IMQ-induced psoriasis-like skin inflammation and enhanced IMQ-induced parakeratosis. Also, Il23-induced ear swelling was diminished in Trex2 knockout mice in comparison with wild-type (wt) mice. Transcriptome analysis identified multiple genes that were deregulated by Trex2 loss after treatment with IMQ. Specifically, immune response genes and pathways normally associated with inflammation were downregulated, whereas those related to skin differentiation and chromatin biology showed increased expression. Interestingly, Trex2 deficiency led to decreased IMQ-induced keratinocyte death via both cell autonomous and noncell autonomous mechanisms. Hence, our data indicate that Trex2 acts as a critical factor in the pathogenesis of psoriasis by promoting keratinocyte apoptosis and enucleation and thereby influencing skin immune responses.

Murine inflammatory caspase-11 has an important role in intestinal epithelial inflammation and barrier function. Activation of the non-canonical inflammasome, mediated by caspase-11, serves as a regulatory pathway for the production of the pro-inflammatory cytokines IL-1β and IL-18, and has a key role in pyroptotic cell death. We have previously demonstrated a protective role for caspase-11 during dextran sulphate sodium (DSS)-induced colitis, however the importance of caspase-11 during colorectal tumour development remains unclear. Here, we show that Casp11 −/− mice are highly susceptible to the azoxymethane (AOM)-DSS model of colitis-associated cancer (CAC), compared to their wild type (WT) littermates. We show that deficient IL-18 production occurs at initial inflammation stages of disease, and that IL-1β production is more significantly impaired in Casp11 −/− colons during established CAC. We identify defective STAT1 activation in Casp11 −/− colons during disease progression, and show that IL-1β signalling induces caspase-11 expression and STAT1 activation in primary murine macrophages and intestinal epithelial cells. These findings uncover an anti-tumour role for the caspase-11 and the non-canonical inflammasome during CAC, and suggest a critical role for caspase-11, linking IL-1β and STAT1 signalling pathways.

Objective— Voltage-dependent K + (Kv) channels from the Kv7 family are expressed in blood vessels and contribute to cardiovascular physiology. Although Kv7 channel blockers trigger muscle contractions, Kv7 activators act as vasorelaxants. Kv7.1 and Kv7.5 are expressed in many vessels. Kv7.1 is under intense investigation because Kv7.1 blockers fail to modulate smooth muscle reactivity. In this study, we analyzed whether Kv7.1 and Kv7.5 may form functional heterotetrameric channels increasing the channel diversity in vascular smooth muscles. Approach and Results— Kv7.1 and Kv7.5 currents elicited in arterial myocytes, oocyte, and mammalian expression systems suggest the formation of heterotetrameric complexes. Kv7.1/Kv7.5 heteromers, exhibiting different pharmacological characteristics, participate in the arterial tone. Kv7.1/Kv7.5 associations were confirmed by coimmunoprecipitation, fluorescence resonance energy transfer, and fluorescence recovery after photobleaching experiments. Kv7.1/Kv7.5 heterotetramers were highly retained at the endoplasmic reticulum. Studies in HEK-293 cells, heart, brain, and smooth and skeletal muscles demonstrated that the predominant presence of Kv7.5 stimulates release of Kv7.1/Kv7.5 oligomers out of lipid raft microdomains. Electrophysiological studies supported that KCNE1 and KCNE3 regulatory subunits further increased the channel diversity. Finally, the analysis of rat isolated myocytes and human blood vessels demonstrated that Kv7.1 and Kv7.5 exhibited a differential expression, which may lead to channel diversity. Conclusions— Kv7.1 and Kv7.5 form heterotetrameric channels increasing the diversity of structures which fine-tune blood vessel reactivity. Because the lipid raft localization of ion channels is crucial for cardiovascular physiology, Kv7.1/Kv7.5 heteromers provide efficient spatial and temporal regulation of smooth muscle function. Our results shed light on the debate about the contribution of Kv7 channels to vasoconstriction and hypertension.