Andrea Telek

A Hot New Twist to Hair Biology: Involvement of Vanilloid Receptor-1 (VR1/TRPV1) Signaling in Human Hair Growth Control

The vanilloid receptor-1 (VR1, or transient receptor potential vanilloid-1 receptor, TRPV1) is activated by capsaicin, the key ingredient of hot peppers. TRPV1 was originally described on sensory neurons as a central integrator of various nociceptive stimuli. However, several human skin cell populations are also now recognized to express TRPV1, but with unknown function. Exploiting the human hair follicle (HF) as a prototypic epithelial-mesenchymal interaction system, we have characterized the HF expression of TRPV1 in situ and have examined TRPV1 signaling in organ-cultured human scalp HF and outer root sheath (ORS) keratinocytes in vitro. TRPV1 immunoreactivity was confined to distinct epithelial compartments of the human HF, mainly to the ORS and hair matrix. In organ culture, TRPV1 activation by capsaicin resulted in a dose-dependent and TRPV1-specific inhibition of hair shaft elongation, suppression of proliferation, induction of apoptosis, premature HF regression (catagen), and up-regulation of intrafollicular transforming growth factor-beta(2). Cultured human ORS keratinocytes also expressed functional TRPV1, whose stimulation inhibited proliferation, induced apoptosis, elevated intracellular calcium concentration, up-regulated known endogenous hair growth inhibitors (interleukin-1beta, transforming growth factor-beta(2)), and down-regulated known hair growth promoters (hepatocyte growth factor, insulin-like growth factor-I, stem cell factor). These findings strongly support TRPV1 as a significant novel player in human hair growth control, underscore the physiological importance of TRPV1 in human skin beyond nociception, and identify TRPV1 as a promising, novel target for pharmacological manipulations of epithelial growth disorders.

Inhibition of human hair follicle growth by endo- and exocannabinoids

Recent studies strongly suggest that the cannabinoid system is a key player in cell growth control. Since the organ‐culture of human hair follicles (HF) offers an excellent, clinically relevant model for complex tissue interaction systems, we have asked whether the cannabinoid system plays a role in hair growth control. Here, we show that human scalp HF, intriguingly, are both targets and sources of endocan‐nabinoids. Namely, the endocannabinoid N‐arachido‐noylethanolamide (anandamide, AEA) as well as the exocannabinnoid Δ (9)‐tetrahydrocannabinol dose‐de‐pendently inhibited hair shaft elongation and the proliferation of hair matrix keratinocytes, and induced intraepithelial apoptosis and premature HF regression (catagen). These effects were inhibited by a selective antagonist of cannabinoid receptor‐1 (CB1). In contrast to CB2, CB1 was expressed in a hair cycle‐dependent manner in the human HF epithelium. Since we successfully identified the presence of endocannabinoids in human HF, our data strongly suggest that human HF exploit a CB1‐mediated endocannabinoid signaling system for negatively regulating their own growth. Clinically, CB1 agonists may therefore help to manage unwanted hair growth, while CB1 antagonists might counteract hair loss. Finally, human HF organ culture offers an instructive, physiologically relevant new research tool for dissecting “nonclassical” effects of endocannabinoids and their receptor‐mediated signaling in general.—Telek, A., Bíró, T., Bodó, E., Tóth, B. I., Borbíró, I., Kunos, G., Paus, R. Inhibition of human hair follicle growth by endo‐ and exocannabi‐noids. FASEB J. 21, 3534–3541 (2007)

Mitochondrial expression of the two-pore domain TASK-3 channels in malignantly transformed and non-malignant human cells

The presence of TASK-3 channels has been described in a number of healthy and malignantly transformed cells, showing mainly intracellular distribution with relatively insignificant labelling of the cell surface membrane. In this work, immunochemical and molecular biology methods were utilised to establish the intracellular organelle whose TASK-3 expression accounts for this strong intracellular labelling using cultured melanoma and HaCaT cells. Before the immunocytochemical experiments, the presence of TASK-3 mRNA was also confirmed in melanoma cells. Comparison of the results of the TASK-3- and mitochondrion-specific labelling indicated that the TASK-3 channel subunits were strongly expressed by mitochondria in both investigated cell types. Moreover, prominent TASK-3 expression of keratinocytes could also be demonstrated in histological sections excised from the human skin. These results indicate that TASK-3 channels are present in the mitochondria in both malignantly transformed and healthy cells, suggesting that they might have roles in ensuring mitochondrial functions.

The synthetic bryostatin analog Merle 23 dissects distinct mechanisms of bryostatin activity in the LNCaP human prostate cancer cell line

Bryostatin 1 has attracted considerable attention both as a cancer chemotherapeutic agent and for its unique activity. Although it functions, like phorbol esters, as a potent protein kinase C (PKC) activator, it paradoxically antagonizes many phorbol ester responses in cells. Because of its complex structure, little is known of its structure-function relations. Merle 23 is a synthetic derivative, differing from bryostatin 1 at only four positions. However, in U-937 human leukemia cells, Merle 23 behaves like a phorbol ester and not like bryostatin 1. Here, we characterize the behavior of Merle 23 in the human prostate cancer cell line LNCaP. In this system, bryostatin 1 and phorbol ester have contrasting activities, with the phorbol ester but not bryostatin 1 blocking cell proliferation or tumor necrosis factor alpha secretion, among other responses. We show that Merle 23 displays a highly complex pattern of activity in this system. Depending on the specific biological response or mechanistic change, it was bryostatin-like, phorbol ester-like, intermediate in its behavior, or more effective than either. The pattern of response, moreover, varied depending on the conditions. We conclude that the newly emerging bryostatin derivatives such as Merle 23 provide powerful tools to dissect subsets of bryostatin mechanism and response.

Inhibition of TASK-3 (KCNK9) channel biosynthesis changes cell morphology and decreases both DNA content and mitochondrial function of melanoma cells maintained in cell culture.

TASK-3 channel overexpression was shown to facilitate the survival of malignantly transformed cells, possibly by providing greater hypoxia tolerance through a still unknown mechanism. Although it has been suggested previously that TASK-3 channels are expressed in the mitochondrial membranes, their role here remains elusive. In this study, a transient transfection of TASK-3 knockdown melanoma cell cultures was produced to show the significance of TASK-3 expression. Reduction of the TASK-3 protein biosynthesis induced characteristic changes in cell morphology, reduced the amount of DNA and decreased metabolic activity and mitochondrial function of melanoma cells when compared with control. These findings indicate that TASK-3 channel expression and function is indispensable for the proliferation and/or survival of the melanoma cells, as they seem to contribute to their mitochondrial functions. The significance is that, in this study, we have shown that TASK-3 channels are expressed in the mitochondria of melanoma malignum cells, and they are essential for maintaining cellular integrity and viability. The TASK-3 knockdown melanoma cell line had altered morphology, reduced DNA content, decreased metabolic activity and impaired mitochondrial function. These data indicate that TASK-3 channels are functionally present in the mitochondria of the melanoma cells, and their function is essential for the survival of these cells, thus TASK-3 channels may be the possible targets of future anticancer therapy.

Hypotonic stress influence the membrane potential and alter the proliferation of keratinocytes in vitro

Abstract:  Keratinocyte proliferation and differentiation is strongly influenced by mechanical forces. We investigated the effect of osmotic changes in the development of HaCaT cells in culture using intracellular calcium measurements, electrophysiological recordings and molecular biology techniques. The application of hypotonic stress (174 mOsmol/l) caused a sustained hyperpolarization of HaCaT cells from a resting potential of −27 ± 4 to −51 ± 9 mV. This change was partially reversible. The surface membrane channels involved in the hyperpolarization were identified as chloride channels due to the lack of response in the absence of the anion. Cells responded with an elevation of intracellular calcium concentration to hypotonic stress, which critically depended on external calcium. The presence of phorbol‐12‐myristate‐13‐acetate in the culture medium for 12 h augmented the subsequent response to hypotonic stress. A sudden switch from iso‐ to hypotonic solution increased cell proliferation and suppressed the production of involucrin, filaggrin and transglutaminase, markers of keratinocyte differentiation. It is concluded that sudden mechanical forces increase the proliferation of keratinocytes through alterations in their membrane potential and intracellular calcium concentration. These changes together with additional modifications in channel expression and intracellular signalling mechanisms could underlie the increased proliferation of keratinocytes in hyperproliferative skin diseases.

Comparison of transcriptional response to phorbol ester, bryostatin 1, and bryostatin analogs in LNCaP and U937 cancer cell lines provides insight into their differential mechanism of action.

Bryostatin 1, like the phorbol esters, binds to and activates protein kinase C (PKC) but paradoxically antagonizes many but not all phorbol ester responses. Previously, we have compared patterns of biological response to bryostatin 1, phorbol ester, and the bryostatin 1 derivative Merle 23 in two human cancer cell lines, LNCaP and U937. Bryostatin 1 fails to induce a typical phorbol ester biological response in either cell line, whereas Merle 23 resembles phorbol ester in the U937 cells and bryostatin 1 in the LNCaP cells. Here, we have compared the pattern of their transcriptional response in both cell lines. We examined by qPCR the transcriptional response as a function of dose and time for a series of genes regulated by PKCs. In both cell lines bryostatin 1 differed primarily from phorbol ester in having a shorter duration of transcriptional modulation. This was not due to bryostatin 1 instability, since bryostatin 1 suppressed the phorbol ester response. In both cell lines Merle 23 induced a pattern of transcription largely like that of phorbol ester although with a modest reduction at later times in the LNCaP cells, suggesting that the difference in biological response of the two cell lines to Merle 23 lies downstream of this transcriptional regulation. For a series of bryostatins and analogs which ranged from bryostatin 1-like to phorbol ester-like in activity on the U937 cells, the duration of transcriptional response correlated with the pattern of biological activity, suggesting that this may provide a robust platform for structure activity analysis.

Some phorbol esters might partially resemble bryostatin 1 in their actions on LNCaP prostate cancer cells and U937 leukemia cells.

Phorbol 12‐myristate 13‐acetate (PMA) and bryostatin 1 are both potent protein kinase C (PKC) activators. In LNCaP human prostate cancer cells, PMA induces tumor necrosis factor alpha (TNFα) secretion and inhibits proliferation; bryostatin 1 does not, and indeed blocks the response to PMA. This difference has been attributed to bryostatin 1 not localizing PKCδ to the plasma membrane. Since phorbol ester lipophilicity influences PKCδ localization, we have examined in LNCaP cells a series of phorbol esters and related derivatives spanning some eight logs in lipophilicity (logP) to see if any behave like bryostatin 1. The compounds showed marked differences in their effects on proliferation and TNFα secretion. For example, maximal responses for TNFα secretion relative to PMA ranged from 97 % for octyl‐indolactam V to 24 % for phorbol 12,13‐dibenzoate. Dose–response curves ranged from monophasic for indolactam V to markedly biphasic for sapintoxin D. The divergent patterns of response, however, correlated neither to lipophilicity, to plasma membrane translocation of PKCδ, nor to the ability to interact with model membranes. In U937 human leukemia cells, a second system in which PMA and bryostatin 1 have divergent effects, viz. PMA but not bryostatin 1 inhibits proliferation and induces attachment, all the compounds acted like PMA for proliferation, but several induced a reduced level or a biphasic dose–response curve for attachment. We conclude that active phorbol esters are not all equivalent. Depending on the system, some might partially resemble bryostatin 1 in their behavior; this encourages the concept that bryostatin‐like behavior may be obtained from other structural templates.

Altered calcium handling following the recombinant overexpression of protein kinase C isoforms in HaCaT cells

Abstract:  Both changes in intracellular calcium concentration ([Ca2+]i) and activation of certain protein kinase C (PKC) isoforms play a crucial role in keratinocyte functions. To better understand the interaction between these two signalling pathways we investigated the resting [Ca2+]i and the extracellular ATP‐induced changes in [Ca2+]i on HaCaT cell clones overexpressing either the classical α or the β PKC isoform. These PKC isoenzymes were previously shown to decrease (α) or increase (β) cell proliferation and augment (α) or suppress (β) cell differentiation. Keratinocyte clones with decreased proliferation rate were found to have unaltered resting [Ca2+]i, but responded with greater calcium transients to the application of 180 μm of ATP. In contrast, clones with increased proliferation rate had elevated resting [Ca2+]i and suppressed calcium responses to ATP. Calcium transients on PKCβ clones displayed a faster falling phase. Each clone had a distinct purinergic receptor expression pattern, some of which paralleled the altered proliferation rate and calcium handling. Keratinocytes overexpressing PKCβ revealed decreased P2X1 and increased P2Y1 receptor expression as compared with the control or PKCα clones. The expression level of P2X7 was significantly increased in keratinocytes overexpressing PKCα. On the other hand neither the P2X2 nor the P2Y2 expression was altered significantly in the cell types investigated. These data indicate that a modified proliferation and differentiation pattern is associated with altered calcium handling in keratinocytes. The observations also suggest that different PKC isoenzymes have different effects on the phosphatidyl–inositol signalling pathway.

Conformationally Constrained Analogues of Diacylglycerol (DAG). 31. Modulation of the Biological Properties of Diacylgycerol Lactones (DAG-lactones) Containing Rigid-Rod Acyl Groups Separated from the Core Lactone by Spacer Units of Different Lengths

Diacylglycerol lactones built with a rigid 4-[(methylphenyl)ethynyl]phenyl rod that is separated from the exocyclic acylcarbonyl of the DAG-lactone core by a spacer unit of variable length were synthesized and studied. Binding affinities for a panel of classical and novel PKC isozymes in two different phospholipid environments, one corresponding to the plasma membrane of cells, were determined. The kinetics and site of translocation for the PKC isozymes α and δ upon treatment with the compounds were also studied as well as the early response of ERK phosphorylation and the late response of induction of apoptosis in the human prostatic carcinoma cell line LNCaP. Finally, the compounds were evaluated in terms of their interaction with biomimetic lipid/polydiacetylene membranes by the associated chromatic response. The different spatial disposition of the rigid structural motif on the DAG-lactones contributes to differential activity.