Retinoid signaling regulates breast cancer stem cell differentiation

The cancer stem cell (CSC) hypothesis implicates the development of new therapeutic approaches to target the CSC population. Characterization of the pathways that regulate CSCs activity will facilitate the development of targeted therapies. We recently reported that the enzymatic activity of ALDH1, as measured by the ALDELFUOR assay, can be utilized to isolate normal and malignant breast stem cells in both primary tumors and cell lines. In this study, utilizing a tumorsphere assay, we have demonstrated the role of retinoid signaling in the regulation of breast CSCs self-renewal and differentiation. Utilizing the gene set enrichment analysis (GSEA) algorithm we identified gene sets and pathways associated with retinoid signaling. These pathways regulate breast CSCs biology and their inhibition may provide novel therapeutic approaches to target breast CSCs.     

Overexpression of the calcium sensing receptor accelerates epidermal differentiation and permeability barrier formation in vivo

The calcium sensing receptor (CaSR) has emerged as an important mediator of a wide range of Ca(2+)-dependent physiological responses (Ca(2+) signaling) in various tissues. To explore the role of CaSR in the epidermis, we utilised the keratin 14 promoter to express CaSR cDNA constitutively in the basal cells of the stratified squamous epithelium of transgenic mice. Analysis of the transgenic mice revealed that a sensitized response to CaSR signaling accelerates the epidermal differentiation program with the precocious formation of the epidermal permeability barrier (EPB) during development and an accelerated hair growth at birth. Our observations indicate that overexpression of CaSR in the undifferentiated basal cells leads to changes in the differentiation program of the transgenic epidermis, including the stimulation of keratins 1 and 6 as well as the overexpression of several markers of terminal differentiation such as filaggrin, loricrin and involucrin. Our data suggest that the observed modifications in the differentiation pathway are a consequence of a CaSR-induced enhancement of Ca(2+) signaling involving cross-talk with other signaling pathways (e.g. EGF and Wnt/Ca(2+)). These studies provide new insights into the role of CaSR in epidermal differentiation including EPB development and hair follicle morphogenesis.     

Role of the Cldn6 cytoplasmic tail domain in membrane targeting and epidermal differentiation in vivo

It is widely recognized that the claudin (Cldn) family of four tetraspan transmembrane proteins is crucial for tight junction assembly and permeability barrier function; however, the precise role of the tail and loop domains in Cldn function is not understood. We hypothesized that the cytoplasmic tail domain of Cldn6 is crucial for membrane targeting and hence epidermal permeability barrier (EPB) formation. To test this hypothesis via a structure-function approach, we generated a tail deletion of Cldn6 (CDelta187) and evaluated its role in epidermal differentiation and EPB formation through its forced expression via the involucrin (Inv) promoter in the suprabasal compartment of the transgenic mouse epidermis. Even though a functional barrier formed, Inv-CDelta187 mice displayed histological and biochemical abnormalities in the epidermal differentiation program and stimulation of epidermal cell proliferation in both the basal and suprabasal compartments of the interfolliclar epidermis, leading to a thickening of the epidermis after 1 week of age that persisted throughout life. Although some membrane localization was evident, our studies also revealed a significant amount of not only Cldn6 but also Cldn10, Cldn11, and Cldn18 in the cytoplasm of transgenic epidermal cells as well as the activation of a protein-unfolding pathway. These findings demonstrate that the overexpression of a tail truncation mutant of Cldn6 mislocalizes Cldn6 and other Cldn proteins to the cytoplasm and triggers a postnatal increase in proliferation and aberrant differentiation of the epidermis, emphasizing the importance of the Cldn tail domain in membrane targeting and function in vivo.     

Retinoid suppression of transglutaminase activity and envelope competence in cultured human epidermal carcinoma cells

Growth of SCC-13 squamous carcinoma cultures in the presence of retinoids considerably reduced the expression of two differentiation markers, the cellular capability to form cross-linked envelopes, and the enzyme transglutaminase required for cross-linking. A limited survey of retinoids showed that all-trans retinoic acid, 13-cis retinoic acid, and arotinoid Ro 13-6298 were highly effective in the absence of hydrocortisone and were only slightly antagonized by its presence in the medium. In contrast, retinyl acetate, retinol, and retinol bound to its plasma binding protein were quite active in the absence of hydrocortisone but were essentially inactive in its presence. Dexamethasone was also highly effective in antagonizing the suppressive action of retinyl acetate on envelope formation, while the corticosteroid antagonists cortexolone and progesterone were inactive. These results suggest that there are separate pathways, which are differentially regulated by hydrocortisone, for either the metabolism or action of retinol and retinoic acid in SCC-13 cells.     

Apoptosis and differentiation of epidermal keratinocytes

We compared some processes characteristic for both apoptosis and terminal differentiation of epidermal keratinocytes. It can be proposed that nonapoptotic programmed cell death takes place during differentiation of keratinocytes. Apoptosis and terminal differentiation of keratinocytes appear to be different events but some similar molecular mechanisms are involved in both processes.__________Translated from Ontogenez, Vol. 36, No. 2, 2005, pp. 85–89.Original Russian Text Copyright © 2005 by Terskikh, Vasilev.     

Apoptosis and differentiation of epidermal keratinocytes

We compared some processes characteristic for both apoptosis and terminal differentiation of epidermal keratinocytes. It can be proposed that nonapoptotic programmed cell death takes place during differentiation of keratinocytes. Apoptosis and terminal differentiation of keratinocytes appear to be different processes but some similar molecular mechanisms are involved in these processes.     

Cell growth and differentiation in Arabidopsis epidermal cells

Plant epidermal cells are morphologically diverse, differing in size, shape, and function. Their unique morphologies reflect the integral function each cell performs in the organ to which it belongs. Cell morphogenesis involves multiple cellular processes acting in concert to create specialized shapes. The Arabidopsis epidermis contains numerous cell types greatly differing in shape, size, and function. Work on three types of epidermal cells, namely trichomes, root hairs, and pavement cells, has made significant progress towards understanding how plant cells reach their final morphology. These three cell types have highly distinct morphologies and each has become a model cell for the study of morphological processes. A growing body of knowledge is creating a picture of how endoreduplication, cytoskeletal dynamics, vesicle transport, and small GTPase signalling, work in concert to create specialized shapes. Similar mechanisms that determine cell shape and polarity are shared between these cell types, while certain mechanisms remain specific to each.     

Intersectin 1 forms a complex with adaptor protein Ruk/CIN85 in vivo independently of epidermal growth factor stimulation

Intersectin 1 (ITSN1) is an adaptor protein involved in clathrin-mediated endocytosis, apoptosis, signal transduction and cytoskeleton organization. Here, we show that ITSN1 forms a complex with adaptor protein Ruk/CIN85, implicated in downregulation of receptor tyrosine kinases. The interaction is mediated by the SH3A domain of ITSN1 and the third or fourth proline-rich blocks of Ruk/CIN85, and does not depend on epidermal growth factor stimulation, suggesting a constitutive association of ITSN1 with Ruk/CIN85. Moreover, both proteins colocalize in MCF-7 cells with their common binding partner, the ubiquitin ligase c-Cbl. The possible biological role of the interaction between ITSN1 and Ruk/CIN85 is discussed.     

The role of the calcium-sensing receptor in epidermal differentiation

Calcium regulates the proliferation and differentiation of keratinocytes both in vivo and in vitro. Elevated extracellular Ca2+ concentration ([Ca2+]o) raises the intracellular free calcium ([Ca2+]i) and activates differentiation-related genes. Cells lacking the calcium-sensing receptor (CaR) fail to respond to [Ca2+]o and to differentiate, indicating a role for CaR in keratinocyte differentiation. These concepts derived from in vitro experiments have been tested and confirmed in two mouse models.     

Inhibitory epidermal pentapeptide modulates proliferation and differentiation of transformed mouse epidermal cells in vitro.

A transformed mouse epidermal cell line ("308 cells") and nontransformed rat tongue squamous epithelial cells ("RT10 cells") were treated 3 times weekly for a period of two weeks with relatively large doses (150 micrograms/ml) of a synthetic inhibitory epidermal pentapeptide; pyroGlu-Glu-Asp-Ser-GlyOH. The peptide was recently isolated from mouse skin extracts and inhibits normal epidermal cells in vivo and in vitro at a restricted and low dose level. Repeated treatments with the large dose was followed by a 30-40% reduction in the number of 308 cells per well, starting as early as day 1. The number of RT10 cells was reduced about 20% only at termination of the experiment on day 14. In contrast to this, the number of unattached cornified envelopes on day 10 in the RT10 cells was increased by 85%, while the number of cornified, unattached 308 cells was similar to that in the controls. The effects of the pentapeptide thus seem to affect differentiation stronger than proliferation in the nontransformed cell line. Bivariate BrdUrd/DNA flow cytometry analysis on day 10 indicated that the reduced number of 308 cells was mainly due to a slower rate of cell proliferation and not to a increased sloughing off of keratinized cells. This analysis also demonstrated that an inhibition of DNA synthesis in the RT10 cells could be detected prior to a reduction of the cell number per well.