Thyroid Hormones and Gamma Interferon Specifically Increase K15 Keratin Gene Transcription

Abstract

Basal layers of stratified epithelia express keratins K5, K14, and K15, which assemble into intermediate filament networks. Mutations in K5 or K14 genes cause epidermolysis bullosa simplex (EBS), a disorder with blistering in the basal layer due to cell fragility. Nonkeratinizing stratified epithelia, e.g., in the esophagus, produce more keratin K15 than epidermis, which alleviates the esophageal symptoms in patients with K14 mutations. Hypothesizing that increasing the cellular content of K15 could compensate for the mutant K14 and thus ease skin blistering in K14 EBS patients, we cloned the promoter of the K15 gene and examined its transcriptional regulation. Using cotransfection, gel mobility shifts, and DNase I footprinting, we have identified the regulators of K15 promoter activity and their binding sites. We focused on those that can be manipulated with extracellular agents, transcription factors C/EBP, AP-1, and NF-B, nuclear receptors for thyroid hormone, retinoic acid, and glucocorticoids, and the cytokine gamma interferon (IFN-␥). We found that C/EBP-␤ and AP-1 induced, while retinoic acid, glucocorticoid receptors, and NF-B suppressed, the K15 promoter, along with other keratin gene promoters. However, the thyroid hormone and IFN-␥ uniquely and potently activated the K15 promoter. Using these agents, we could boost the amounts of K15 in human epidermis. Our findings suggest that treatments based on thyroid hormone and IFN-␥ could become effective agents in therapy for patients with EBS.

Epidermolysis bullosa simplex: a paradigm for disorders of tissue fragility

“…However, corrective intervention directed at the genetic code per se may not be practical as an effective means of treatment. One way to build up mechanical resiliency in trauma-sensitive epidermis (45) might be to exploit the partial functional redundancy known to exist among select keratins (101)(102)(103) and other IF proteins (104,105) and to devise means to stimulate their endogenous expression in the skin of affected patients.…”

Impact de l'interféron gamma sur la production de la kératine 15 dans les kératinocytes isolés de la peau de patients atteints d'épidermolyse bulleuse simplex /

“…IFN-y also affects other keratins such as K16 in healthy keratinocytes as it was reported by Barker et al, 1993. In contrast to K14, K5 and K15 which are principally produced in basal layer, K17 is only expressed in the suprabasal layer (Radoja et al, 2004) and therefore the replacement of K14 by K17 in EBS is not possible. Radoja et al, (2004) have reported that K15 is induced at the transcriptional level by IFN-y.…”

“…In contrast to K14, K5 and K15 which are principally produced in basal layer, K17 is only expressed in the suprabasal layer (Radoja et al, 2004) and therefore the replacement of K14 by K17 in EBS is not possible. Radoja et al, (2004) have reported that K15 is induced at the transcriptional level by IFN-y. They suggested that the production of K15 could remedy to cytoskeleton defects in EBS harboring KRT14 mutations by forming heterodimers withK5.…”

“…Pour cela, la recherche se base sur des molécules à effet thérapeutique documenté afin de réduire ou même éliminer les agrégats protéiques causés par le mauvais appariement des kératines. En effet l'étude de Radoja et al, en 2004 a rapporté que dans les cellules HeLa, l'utilisation de l'IFN-y stimulerait la production de Kl5 appartenant à la même famille que la K14 et qui pourrait la remplacer en formant des hétérodimères avec K5 (Radoja et al, 2004).…”

“…IL-1 and TNF-a are the activators of NF-KB where the loss of the expression of K15 is observed Radoja et al, 2004). IFN-y also activates NF-KB which will decrease the phosphorylation of STAT1/3 in tumorigenic mouse lung epithelial (LM2) cells .…”