Pannexin 1 and pannexin 3 channels regulate skeletal muscle myoblast proliferation and differentiation.

Pannexins constitute a family of three glycoproteins (Panx1, -2, and -3) forming single membrane channels. Recent work demonstrated that Panx1 is expressed in skeletal muscle and involved in the potentiation of contraction. However, Panxs functions in skeletal muscle cell differentiation, and proliferation had yet to be assessed. We show here that Panx1 and Panx3, but not Panx2, are present in human and rodent skeletal muscle, and their various species are differentially expressed in fetal versus adult human skeletal muscle tissue. Panx1 levels were very low in undifferentiated human primary skeletal muscle cells and myoblasts (HSMM) but increased drastically during differentiation and became the main Panx expressed in differentiated cells. Using HSMM, we found that Panx1 expression promotes this process, whereas it was impaired in the presence of probenecid or carbenoxolone. As for Panx3, its lower molecular weight species were prominent in adult skeletal muscle but very low in the fetal tissue and in undifferentiated skeletal muscle cells and myoblasts. Its overexpression (∼43-kDa species) induced HSMM differentiation and also inhibited their proliferation. On the other hand, a ∼70-kDa immunoreactive species of Panx3, likely glycosylated, sialylated, and phosphorylated, was highly expressed in proliferative myoblasts but strikingly down-regulated during their differentiation. Reduction of its endogenous expression using two Panx3 shRNAs significantly inhibited HSMM proliferation without triggering their differentiation. In summary, our results demonstrate that Panx1 and Panx3 are co-expressed in human skeletal muscle myoblasts and play a pivotal role in dictating the proliferation and differentiation status of these cells.

Cicatricial ectropion in grzybowski type of multiple eruptive keratoacanthomas.

A 41-year-old woman previously diagnosed with generalized eruptive keratoacanthomas of Grzybowski type presented with bilateral lower eyelid cicatrical ectropions. She had previously undergone multiple resections of syringomatous adenomas of both nipples, facial keratoacanthomas, and a lower left lip squamous cell carcinoma. Her facial and periocular skin was thickened with a cobblestone appearance. Cicatricial ectropions involved both upper and lower eyelids. Donor skin was harvested from the dorsum of the foot as this was the only disease-free area on her body, and she achieved a stable result with reduced tearing and improved appearance.

Pannexin1 and Pannexin3 exhibit distinct localization patterns in human skin appendages and are regulated during keratinocyte differentiation and carcinogenesis.

Having shown that Panx1 and Panx3 are expressed in the epidermis, we investigated their distribution in human skin adnexal structures and skin cancer. Both proteins were found in hair follicles, sebaceous and eccrine glands, as well as blood vessels. Panx1 was detected as punctate or diffuse intracellular labeling, while Panx3 was only observed as diffuse intracellular staining, suggesting different functions. We also identified the Panx3 immunoreactive ~70 kD species modulated during keratinocyte differentiation as Panx3. Since our data indicate that pannexins are regulated during keratinocyte differentiation, we assessed whether their levels are altered under circumstances in which keratinocyte differentiation is compromised. We found that Panx1 and Panx3 levels are highly reduced in human keratinocyte tumors, thus showing for the first time that both pannexins are dysregulated in human cancers. Altogether, these data suggest that Panx1 and Panx3 have distinct and unique functions within the skin in health and disease.

The tumor-suppressive function of Connexin43 in keratinocytes is mediated in part via interaction with caveolin-1.

Connexin43 (Cx43) is known to have tumor-suppressive effects, but the underlying mechanisms are still poorly understood. In keratinocytes, we previously showed that the COOH-terminal domain of Cx43 directly interacts with the tumor suppressor Cav-1. We now show that rat epidermal keratinocytes (REK) that are reduced in Cx43 present features of epithelial-to-mesenchymal transition and are more invasive than their control counterparts, whereas overexpression of Cx43 inhibited the 12-O-tetradecanoyl-phorbol-13-acetate (TPA)- and epidermal growth factor (EGF)-induced invasive properties. Carbenoxolone did not alter the inhibitory effect of Cx43 against TPA- and EGF-induced cell invasion, indicating the involvement of a gap junctional intercellular communication-independent mechanism. Interestingly, the association of Cx43 with Cav-1 was found to be reduced after TPA and EGF treatment. Accordingly, the colocalization of Cx43 with Cav-1 was diminished in cells from a human epidermal squamous cell carcinoma, as well as in sections from human keratinocyte tumors, suggesting that Cx43/Cav-1 interaction plays a protective role against keratinocyte transformation. As opposed to cells that overexpress Cx43-GFP, invasion could be induced in rat epidermal keratinocytes that overexpressed a GFP-tagged truncated mutant of Cx43 (Delta244-GFP) that we previously showed not to interact with Cav-1, as well as in cells that overexpressed Cx43-GFP but were reduced in Cav-1. Our data show that Cx43 possesses tumor-suppressive properties in keratinocytes and provide the first evidence that the Cx43/Cav-1 interaction is altered in keratinocyte transformation processes, as well as in human keratinocyte tumors, and that this association might play a role in Cx43-mediated tumor suppression.

Modification of the forearm tourniquet techniques of intravenous regional anaesthesia for operations on the distal forearm and hand.

Our aim was to find out if a modified intravenous regional anaesthetic block technique, used for invasive surgical procedures on the distal forearm and hand, results in a drier operative field than traditional methods. Twenty consenting adult (age > 18) patients who were to have an operation on the distal forearm or hand were randomised into two groups (n=10 in each). The first group was using a traditional bier block, with a double upper arm tourniquet. The second group was using a modified regional anaesthetic block technique, with a single upper arm tourniquet, and a single forearm tourniquet. All operative fields were recorded photographically and judged by the operating surgeon as "wet" or "dry". Analgesic requirements and subjective pain were recorded. Plasma lignocaine concentrations were measured. "Wet" operative fields were seen in 6 of the conventional and 0 of the modified group (p=0.01). Patients in the modified group were more comfortable during the procedures (p=0.004). This benefit was not sustained postoperatively (p=0.57). Plasma lignocaine concentrations were higher in the conventional group (p=0.004). The modified technique was as safe as the conventional technique but has the benefits of a drier surgical field and improved intraoperative comfort for patients.

Lobular panniculitis at the site of subcutaneous interferon beta injections for the treatment of multiple sclerosis can histologically mimic pancreatic panniculitis. A study of 12 cases.

BACKGROUND: Thrombosis, mucinosis and necrosis are well-described complications of subcutaneous interferon beta injections. METHODS: We report 12 incisional biopsies from subcutaneous interferon beta injection sites in 12 multiple sclerosis (MS) patients from a single neurologist's practice. RESULTS: We identified abscesses (two cases) or induration (two cases) in acute clinical lesions and lipoatrophy (eight cases) in chronic lesions (biopsied over a year after symptom onset at injection sites). Biopsies from three acute lesions showed vascular thrombosis, dermal mucinosis, lobular neutrophilic panniculitis, necrosis, calcification and hemosiderin deposition (biopsied 2 weeks to 2 months after symptom onset). Two cases contained sterile abscesses. Five of the eight chronic cases presented as hard, indurated lipoatrophy with livedo reticularis. Their biopsies showed subcutaneous calcification and lipoatrophy. Biopsies from the early calcific suppurative and late calcific atrophic phases histologically resembled the early and late phases of subcutaneous saponification in pancreatic panniculitis. CONCLUSIONS: Reactions at the site of subcutaneous interferon beta injections are common. Lipoatrophy can be clinically identified in 39 of 85 MS patients (46%) receiving subcutaneous interferon beta injections for 1 year or longer in our practice. A reaction to interferon should be considered in the differential diagnosis of biopsies that show features of pancreatic panniculitis.

Lobular panniculitis at the site of glatiramer acetate injections for the treatment of relapsing-remitting multiple sclerosis. A report of two cases.

Lipoatrophy and localized panniculitis have been described as rare complications of daily subcutaneous glatiramer acetate injections for the treatment of relapsing-remitting multiple sclerosis (MS). We describe the biopsies from two MS patients in a single neurologist's practice who developed clinical lesions of lipoatrophy at the sites of subcutaneous glatiramer acetate injections. These biopsies showed a lobular panniculitis with lipoatrophy that more closely resembled lupus panniculitis than previous reports of localized panniculitis at glatiramer acetate injection sites. In one case, the area of clinical lipoatrophy continued to enlarge for 6 months after stopping glatiramer acetate therapy, before stabilizing at its current size for the last 8 months. Injection site reactions to glatiramer acetate should be considered in the differential diagnosis of biopsies that show a lupus panniculitis-like appearance. Our observations indicate that glatiramer acetate induced panniculitis is common and may continue to progress after therapy has stopped. In this single neurologist's practice, 64% of the patients receiving daily glatiramer acetate injections had clinical evidence of lipoatrophy or panniculitis. Of 100 consecutive patients receiving therapy for MS between February and November 2006, 14 patients were on glatiramer acetate, 9 of whom had clinical lipoatrophy.

Caveolin-1 and -2 interact with connexin43 and regulate gap junctional intercellular communication in keratinocytes.

Connexin43 (Cx43) has been reported to interact with caveolin (Cav)-1, but the role of this association and whether other members of the caveolin family bind Cx43 had yet to be established. In this study, we show that Cx43 coimmunoprecipitates and colocalizes with Cav-1 and Cav-2 in rat epidermal keratinocytes. The colocalization of Cx43 with Cav-1 was confirmed in keratinocytes from human epidermis in vivo. Our mutation and Far Western analyses revealed that the C-terminal tail of Cx43 is required for its association with Cavs and that the Cx43/Cav-1 interaction is direct. Our results indicate that newly synthesized Cx43 interacts with Cavs in the Golgi apparatus and that the Cx43/Cavs complex also exists at the plasma membrane in lipid rafts. Using overexpression and small interfering RNA approaches, we demonstrated that caveolins regulate gap junctional intercellular communication (GJIC) and that the presence of Cx43 in lipid raft domains may contribute to the mechanism modulating GJIC. Our results suggest that the Cx43/Cavs association occurs during exocytic transport, and they clearly indicate that caveolin regulates GJIC.

Pannexin 1 and pannexin 3 are glycoproteins that exhibit many distinct characteristics from the connexin family of gap junction proteins.

Pannexins are mammalian orthologs of the invertebrate gap junction proteins innexins and thus have been proposed to play a role in gap junctional intercellular communication. Localization of exogenously expressed pannexin 1 (Panx1) and pannexin 3 (Panx3), together with pharmacological studies, revealed a cell surface distribution profile and life cycle dynamics that were distinct from connexin 43 (Cx43, encoded by Gja1). Furthermore, N-glycosidase treatment showed that both Panx1 (approximately 41-48 kD species) and Panx3 (approximately 43 kD) were glycosylated, whereas N-linked glycosylation-defective mutants exhibited a decreased ability to be transported to the cell surface. Tissue surveys revealed the expression of Panx1 in several murine tissues--including in cartilage, skin, spleen and brain--whereas Panx3 expression was prevalent in skin and cartilage with a second higher-molecular-weight species present in a broad range of tissues. Tissue-specific localization patterns of Panx1 and Panx3 ranging from distinct cell surface clusters to intracellular profiles were revealed by immunostaining of skin and spleen sections. Finally, functional assays in cultured cells transiently expressing Panx1 and Panx3 were incapable of forming intercellular channels, but assembled into functional cell surface channels. Collectively, these studies show that Panx1 and Panx3 have many characteristics that are distinct from Cx43 and that these proteins probably play an important biological role as single membrane channels.