PTCH mutations in squamous cell carcinoma of the skin

Ultraviolet light exposure is the major risk factor for the development of squamous cell carcinoma in Caucasians. Mutations in the tumor suppressor gene p53 have been identified in both squamous cell carcinomas and basal cell carcinomas. The human homolog of the Drosophila patched gene, has been shown to be mutated in sporadic basal cell carcinomas; however, mutations in the patched gene have not been found in squamous cell carcinoma. In this study, we screened a total of 20 squamous cell carcinoma samples for mutations in the patched gene. Using polymerase chain reaction-single strand conformation polymorphism as an initial screening method, we identified one non-sense mutation, two mis-sense mutations and three silent mutations in five squamous cell carcinoma samples. In one squamous cell carcinoma sample, we identified a tandem GG-->AA transitional change at nucleotide 3152 in exon 18 of the patched gene that resulted in a premature stop codon at codon 1051. The three squamous cell carcinoma samples containing non-sense and mis-sense mutations were isolated from individuals with histories of multiple basal cell carcinoma. Sequence analysis of the p53 gene in these five squamous cell carcinoma samples identified one CC-->TT and three C-->T ultraviolet-specific nucleotide changes. Our study provides evidence that the patched gene is mutated in squamous cell carcinoma from individuals with a history of multiple basal cell carcinoma. The identification of ultraviolet-specific nucleotide changes in both tumor suppressor genes supports the notion that ultraviolet exposure plays an important part in the development of squamous cell carcinoma.

UV-specific p53 and PTCH mutations in sporadic basal cell carcinoma of sun-exposed skin

UVB irradiation is known to produce DNA damage at mutation hotspots in the p53 tumor suppressor gene, leading to the development of skin cancers. Mutations in the PTCH tumor suppressor gene, which is known to be responsible for the development of nevoid basal cell carcinoma syndrome, have also been identified in sporadic basal cell carcinomas (BCCs). We describe the case of an 80-year-old welder in whom 3 novel p53 mutations, as well as UV-specific PTCH mutations, were detected in two BCC samples from sun-exposed skin. The simultaneous presence of UV-specific p53 and PTCH mutations in the same BCC sample has not previously been reported.

Role of PTCH and p53 genes in early-onset basal cell carcinoma

Basal cell carcinoma (BCC) is the most common skin cancer in the Western world. Ultraviolet (UV) exposure, race, age, gender, and decreased DNA repair capacity are known risk factors for the development of BCC. Of these, UVB irradiation from sunlight is the most significant risk factor. The incidence of sporadic BCC increases in individuals older than age 55, with the greatest incidence reported in individuals who are older than 70, and is rare in individuals who are younger than 30. In this study, we analyzed 24 BCC samples from individuals who had BCC diagnosed by the age of 30. Fifteen single-stranded conformation polymorphism variants in the PTCH gene were identified in 13 BCC samples. Sequence analysis of these single-stranded conformation polymorphism variants revealed 13 single nucleotide changes, one AT insertion, and one 15-bp deletion. Most of these nucleotide changes (nine of 15) were predicted to result in truncated PTCH proteins. Fifteen p53 mutations were also found in 11 of the 24 BCC samples. Thirty-three percent (five of 15) and 60% (nine of 15) of the nucleotide changes in the PTCH and p53 genes, respectively, were UV-specific C-->T and CC-->TT nucleotide changes. Our data demonstrate that the p53 and PTCH genes are both implicated in the development of early-onset BCC. The identification of UV-specific nucleotide changes in both tumor suppressor genes suggests that UV exposure is an important risk factor in early onset of BCC.

Germline PTEN mutations in three families with Cowden syndrome

Cowden syndrome (CS) is an autosomal dominant inherited disorder characterized by hamartomas in a variety of tissues including the skin, thyroid, breast, endometrium, and the brain. Individuals with CS are predisposed to development of malignancy in these organs, especially the breast and the thyroid. We describe 3 unrelated individuals with CS associated with germline PTEN mutations. While the frameshift (375insTTTA) and the missense (Gly69Arg) mutations reported herein are novel in CS, the nonsense (Arg130stop) mutation has been described in 2 families with CS and in a single family exhibiting both CS and Bannayan Zonana phenotype.

Absence of PTEN germ-line mutations in men with a potential inherited predisposition to prostate cancer

Epidemiological studies have demonstrated that men with a family history of prostate cancer are at an increased risk for this disease. This important observation has led a number of research teams, including our own, to collect DNA samples and clinical data from prostate cancer families, with the goal of localizing and characterizing prostate cancer susceptibility genes. The candidate tumor suppressor gene PTEN (also called MMAC1) has recently been shown to be somatically altered in several common malignancies, including cancers of the brain, kidney, skin, thyroid, endometrium, breast, and prostate. Germ-line mutations in this gene, which maps to chromosome 10q23, have been associated with Cowden disease, an autosomal dominant cancer predisposition syndrome that is characterized by multiple hamartomas. Although prostate cancer is not typically associated with Cowden disease, previous studies of sporadic prostate cancers demonstrate loss of heterozygosity at 10q23 loci in approximately 25% of cases. We, therefore, hypothesized that germ-line mutations in the PTEN gene may predispose to prostate cancer in a subset of families, particularly those in which cancers of the breast, kidney, and/or thyroid also segregate. To test this hypothesis, DNA was isolated from whole blood of 11 prostate cancer patients from 10 unrelated families. Four of the 10 families met the previously established clinical criteria for hereditary prostate cancer. Eight of the II men had at least one second primary malignancy, including cases of neuroendocrine cancer, glioblastoma multiforme, melanoma, kidney, and thyroid cancer. Although we identified some common as well as some unique polymorphisms, no nonsense or missense mutations were identified in any of the 11 samples. To further examine the possibility that PTEN mutations contribute to prostate cancer predisposition, we also studied the probands from each of 10 families with early-onset and/or multiple individuals with prostate cancer. Sequence analysis of the PTEN gene in these 10 men also revealed no mutations or novel polymorphisms. We conclude that germ-line mutations in the PTEN are unlikely to contribute in a significant way to the inherited predisposition to prostate cancer.

PTEN/MMAC1 mutations in hepatocellular carcinomas

Mutations in the PTEN/MMAC1 gene have been identified in several types of human cancers and cancer cell lines, including brain, endometrial, prostate, breast, thyroid, and melanoma. In this study, we screened a total of 96 hepatocellular carcinoma (HCC) samples from Taiwan, where HCC is the leading cancer in males and third leading cancer in females, for mutations in the PTEN/MMAC1 gene. Complete sequence analysis of these samples demonstrated a missense mutation in exon 5 (K144I) and exon 7 (V255A) from HCC samples B6-21 and B6-2, respectively. A putative splice site mutation was also detected in intron 3 from sample B6-2. Both B6-21 and B6-2 were previously shown to contain missense mutations in the coding sequences of the p53 gene. Functional studies with the two missense mutations demonstrated that while mutation V255A in exon 7 resulted in a loss of phosphatase activity, mutation K144I in exon 5 retained its phosphatase activity. Additionally, we identified a silent mutation (P96P) in exon 5 of the PTEN/MMAC1 gene from HCC sample B6-22. These data provide the first evidence that the PTEN/MMAC1 gene is mutated in a subset of HCC samples.

Phenotypic findings of Cowden syndrome and Bannayan-Zonana syndrome in a family associated with a single germline mutation in PTEN

Cowden syndrome (CS) and Bannayan-Zonana syndrome (BZS) are two hamartoma syndromes with distinct phenotypic features. Although partial clinical overlap exists between CS and BZS, they are considered to be separate entities. PTEN has been identified as the susceptibility gene for both disorders, suggesting allelism. We have identified a germline mutation, R335X, in PTEN in a family consisting of two female members with the phenotypic findings of CS and two male members with the phenotypic findings of BZS. To our knowledge, this is the first report that shows the presence of separate subjects with CS and with BZS in a single family associated with a single germline PTEN mutation.

Identification of PTEN mutations in five families with Bannayan-Zonana syndrome

Germline mutations in PTEN, a putative tumor suppressor gene, has been identified in 2 autosomal dominant inherited hamartoma syndromes, Cowden syndrome (CS) and Bannayan-Zonana syndrome (BZS). While both diseases exhibit distinct phenotypic features, there seems to be a partial clinical overlap between the 2 diseases. To date, 9 families with BZS have been screened for PTEN mutations, of which 5 were found to exhibit mutations in this gene. We report 5 novel germline mutations in the PTEN coding sequence from 5 unrelated families with the BZS phenotype. While all the mutations we identified are novel in BZS, 1003C-->T (nonsense mutation) and 209+5G-->A (putative splice site mutation) have been previously reported in unrelated families with CS and Lhermitte Duclos disease. Interestingly, 1 of the families has an individual with BZS and 1 with CS phenotype, associated with a single PTEN mutation, 885insA. These data support the notion that CS and BZS may be within the spectrum of the same primary disorder.

Severe Lhermitte-Duclos disease with unique germline mutation of PTEN

Germline mutations in the PTEN gene have recently been identified in some individuals with Cowden disease (CD), Lhermitte-Duclos disease (LDD), and Bannayan-Zonana syndrome. We report on a patient with CD and LDD in whom a unique de novo germline missense mutation is present in the PTEN gene. Direct sequence analysis detected a transitional change (T-->C) at nucleotide 335, resulting in substitution of the amino acid proline for leucine. The mutation is in exon 5, which has been proposed as a "hot-spot" for germline mutations. Comparison of this patient's clinical course with the previously reported cases of CD and LDD shows more extensive and more severe clinical findings than reported previously. Findings in this patient contribute to the current understanding of germline PTEN mutations and clinical outcome.

Similarities of cutaneous and breast pathology in Cowden's Syndrome

Cowden's Syndrome (CS), or multiple hamartoma syndrome, is an autosomal dominant disorder characterized by mucocutaneous lesions, multiple benign tumors of internal organs and an increased risk of breast cancer. Here, we describe and illustrate in detail the benign breast pathology of 59 breast cases from 19 women with CS. Fibrosis is a significant characteristic of the breasts of patients with CS. Fibroadenomas appear to hyalinize at an early age and are frequently complex. The specimens demonstrate a spectrum of dense hyalinization of both the lobule and the stroma, and hyaline nodules appear to be the most characteristic lesion. This hyalinization process shares striking similarities with keloids, as well as the sclerotic nodules seen in the skin of CS individuals. Ductal carcinoma in CS was common, and it appeared to be associated with stromal hyalinization. Other frequently found benign features are adenosis and cysts. Of interest, the features of the benign breast disease in CS show certain similarities with senescent lobules, fibrous mastopathy of diabetes mellitus, and mammary hamartomas. These observations provide a framework for pathologists to identify this underrecognized syndrome.

Repression of transactivation of the retinoic acid receptor beta2 promoter in human breast cancer cells

In previous studies, we have shown that the expression of retinoic acid receptor beta2 (RARbeta2) is altered in certain breast cancer cell lines. To investigate the mechanism responsible for this change, we studied in detail the RARbeta2 promoter in cell lines which demonstrated altered expression and compared these results to cell lines in which RARbeta2 was expressed normally. Direct DNA sequencing failed to identify alterations in the sequences of the known response elements in the cell lines manifesting altered expression patterns. By contrast, electrophoretic mobility shift studies of the proteins binding to these response elements demonstrated striking differences in the cells in which expression was altered, when compared to patterns seen in normal cells. Moreover, transient transfection studies using constructs of the RARbeta2 promoter demonstrated an absence of transactivation in the lines in which the expression of this gene was altered. These data suggest that the mechanism responsible for loss of induction of RARbeta2 in breast tumor cells is, at least in part, transcriptional repression.

The genetic basis of Cowden's syndrome: three novel mutations in PTEN/MMAC1/TEP1

Cowden's syndrome (CS) is an autosomal dominant disorder associated with an increased risk of developing benign and malignant tumors in a variety of tissues, including the skin, thyroid, breast and brain. Women with CS are felt to have an increased risk of developing breast cancer, and virtually all women with CS develop bilateral fibrocystic disease of the breast. Recently, a series of germline mutations have been identified from CS families in a gene known as PTEN/MMAC1/TEP1. In this study, we used heteroduplex analysis and direct sequencing analysis and identified three novel germline mutations in the PTEN/MMAC1/TEP1 coding sequence from unrelated individuals with CS. We report a de novo transition (T-->C) at nucleotide 335 in exon 5. This missense mutation resulted in a leucine to proline (CTA to CCA) change at codon 112. We also describe a novel splice site mutation (801+2T-->G) in intron 7 that caused exon skipping in PTEN/MMAC1/TEP1 mRNA. The third mutation we report is a missense mutation, consisting of a transition (T-->C) at nucleotide 202 in exon 3, resulting in a tyrosine to histidine (TAC to CAC) change at codon 68. Finally, we also detected a rare polymorphism in exon 7 of the PTEN/MMAC1/TEP1 coding sequence. These data confirm the observation that mutations of the PTEN/MMAC1/TEP1 coding sequence are responsible for at least some cases of CS, and further define the spectrum of mutations in this autosomal dominant disorder.

Alopecia universalis associated with a mutation in the human hairless gene

There are several forms of hereditary human hair loss, known collectively as alopecias, the molecular bases of which are entirely unknown. A kindred with a rare, recessively inherited type of alopecia universalis was used to search for a locus by homozygosity mapping, and linkage was established in a 6-centimorgan interval on chromosome 8p12 (the logarithm of the odds favoring linkage score was 6.19). The human homolog of a murine gene, hairless, was localized in this interval by radiation hybrid mapping, and a missense mutation was found in affected individuals. Human hairless encodes a putative single zinc finger transcription factor protein with restricted expression in the brain and skin.

Clinical and pathological features of breast disease in Cowden's syndrome: an underrecognized syndrome with an increased risk of breast cancer

Cowden's syndrome (CS), or multiple hamartoma syndrome, is an autosomal dominant disorder associated with benign skin tumors and an increased risk of breast cancer. In an effort to understand the basic mechanisms regulating the development of breast cancer in this patient population, as well as to define diagnostic aspects of the disorder, we describe for the first time the clinical and pathological spectrum of breast disease in CS. We obtained the clinical histories and examined the histopathology of 59 cases from 19 women with CS sent to us from a variety of institutions. The 19 women showed a spectrum of benign histopathological findings, including ductal hyperplasia, intraductal papillomatosis, adenosis, lobular atrophy, fibroadenomas, and fibrocystic change. Seventeen (89%) showed features suggestive of a breast hamartoma. Fourteen women (74%) showed malignant disease, most of which was ductal carcinoma. Twelve patients (86%) showed ductal carcinoma in situ (DCIS), and 12 (86%) showed infiltrating ductal carcinoma. One patient had only DCIS and another patient showed both infiltrating tubular carcinoma and lobular carcinoma in situ. Ten patients (71%) actually showed foci of tumor involving densely fibrotic, hamartomatous areas. In summary, we show that women with CS have a spectrum of exuberant benign and malignant breast pathology. A common benign breast lesion in CS is a densely fibrotic hyalinized nodule, whereas the most frequent breast malignancy is ductal carcinoma.

Patterns of X chromosome inactivation in sporadic basal cell carcinomas: evidence for clonality

BACKGROUND

Some basal cell carcinomas (BCCs) contain genetic mutations, suggesting that the lesion is composed of a monoclonal population of cells. Clonality, a distinguishing feature of neoplasia, can be inferred by referencing clonal markers such as the pattern of X chromosome inactivation. The X-linked human androgen receptor gene (HUMARA; GenBank) contains a polymorphic DNA marker that reliably illustrates the pattern of X chromosome inactivation in a tissue.

OBJECTIVE

Our purpose was to determine the clonality of sporadic BCCs by examining patterns of X chromosome inactivation.

METHODS

The patterns of X chromosome inactivation in paired samples of normal skin and sporadic BCCs from 24 women were compared by means of the HUMARA gene assay.

RESULTS

All samples from normal skin displayed random X chromosome inactivation, consistent with lyonization. In 15 of 25 tumor samples (60%), nonrandom X chromosome inactivation was detected, consistent with monoclonality.

CONCLUSION

At least some sporadic BCCs are composed of a monoclonal population of cells, strengthening the contention that a collection of mutations confers a growth advantage to this epithelial lesion.

The role of MMAC1 mutations in early-onset breast cancer: causative in association with Cowden syndrome and excluded in BRCA1-negative cases

Cowden syndrome (CS) is an autosomal dominant disorder associated with the development of hamartomas and benign tumors in a variety of tissues, including the skin, thyroid, breast, endometrium, and brain. It has been suggested that women with CS are at increased risk for breast cancer. A locus for CS was recently defined on chromosome 10 in 12 families, resulting in the identification of the CS critical interval, between the markers D10S215 and D10S541. More recently, affected individuals in four families with CS have been shown to have germ-line mutations in a gene known as "PTEN," or "MMAC1," which is located in the CS critical interval on chromosome 10. In this study, we report three novel MMAC1 mutations in CS and demonstrate that MMAC1 mutations are associated with CS and breast cancer. Furthermore, we also show that certain families and individuals with CS do not have mutations in the coding sequence of MMAC1. Finally, we did not detect MMAC1 mutations in a subpopulation of individuals with early-onset breast cancer, suggesting that germ-line mutations in this gene do not appear to be common in this group.

Expression of retinoid X receptors in human dermal fibroblasts

Retinoic acid (RA) is known to exert profound effects on growth and differentiation in human dermal fibroblasts. In the observations presented here, we examined the regulation of expression of members of the RXR multigene family in human dermal fibroblasts. We showed that the messenger RNAs for both RXR alpha and RXR beta are expressed in human fibroblasts, but that the messenger RNA for RXR gamma is not detectable in these cells. Electrophoretic mobility shift studies of binding to the beta 2RARE in human dermal fibroblasts demonstrated that a single complex binds to beta 2RARE in the absence of RA. Stimulating cells with all-trans RA induced a second complex. An antibody to the RXR beta protein supershifted both complexes, while an antibody to the RXR alpha S/B protein had no effect on the binding. These data demonstrate that RXR beta plays an important role in retinoid-regulated signal transduction pathways in human dermal fibroblasts and the regulation of expression of the RXR gene family is different from that of the RAR gene family.

Germline mutations of the PTEN gene in Cowden disease, an inherited breast and thyroid cancer syndrome

Cowden disease (CD) is an autosomal dominant cancer predisposition syndrome associated with an elevated risk for tumours of the breast, thyroid and skin. Lhermitte-Duclos disease (LDD) cosegregates with a subset of CD families and is associated with macrocephaly, ataxia and dysplastic cerebellar gangliocytomatosis. The common feature of these diseases is a predisposition to hamartomas, benign tumours containing differentiated but disorganized cells indigenous to the tissue of origin. Linkage analysis has determined that a single locus within chromosome 10q23 is likely to be responsible for both of these diseases. A candidate tumour suppressor gene (PTEN) within this region is mutated in sporadic brain, breast and prostate cancer. Another group has independently isolated the same gene, termed MMAC1, and also found somatic mutations throughout the gene in advanced sporadic cancers. Mutational analysis of PTEN in CD kindreds has identified germline mutations in four of five families. We found nonsense and missense mutations that are predicted to disrupt the protein tyrosine/dual-specificity phosphatase domain of this gene. Thus, PTEN appears to behave as a tumour suppressor gene in the germline. Our data also imply that PTEN may play a role in organizing the relationship of different cell types within an organ during development.

Molecular basis of variegate porphyria: a de novo insertion mutation in the protoporphyrinogen oxidase gene

The porphyrias are disorders that result from the inherited or acquired dysregulation of one of the eight enzymes in the heme biosynthetic pathway. Variegate porphyria (VP) is characterized by deficiencies in protoporphyrinogen oxidase (PPO) and has recently been genetically linked (Z = 6.62) to the PPO gene on chromosome 1q21. In this study, we have identified two sequence variants in the PPO gene in a family with VP. The first is a neutral polymorphism at the -47 position of intron 2; this polymorphism is present in the general population and is unlikely to underlie the VP phenotype. The second is a mutation in the PPO gene in a patient with VP; the mutation consists of an apparently de novo 2-bp insertion in exon 3 of PPO and results in a frameshift and downstream premature termination codon. These data establish that a frameshift mutation in PPO is the underlying mutation in this patient with VP and explain the sporadic occurrence of the phenotype in this family.

Clonality of basal cell carcinoma--molecular analysis of an interesting case

Tumor cells represent a single clone of cells that have undergone a series of mutations in genomic DNA. This process, known as clonal evolution, is a distinguishing feature of cancer. The human androgen receptor gene (HUMARA; GenBank) contains a highly polymorphic cytosine-adenine-guanine trinucleotide repeat that can be used to determine clonality by depicting X chromosome inactivation patterns. Random X chromosome inactivation is consistent with polyclonality; nonrandom X chromosome inactivation indicates a clonal population of cells. Basal cell carcinoma (BCC) demonstrates an atypical growth pattern in that it grows slowly, rarely metastasizes, and is rarely lethal. Whether this tumor results from the accumulation of mutations in a single cell with subsequent clonal expansion or reflects a polyclonal response by a group of cells to a growth stimulus is unknown. To provide further insight into the molecular events characterizing BCCs, we determined the clonal origin of five modular BCCs from a female patient by analyzing X chromosome inactivation patterns at the HUMARA locus. All tumors demonstrated a nonrandom pattern of X chromosome inactivation, consistent with monoclonal proliferation. These findings provide strong genetic evidence that sporadic BCCs develop by clonal evolution and support the contention that a series of mutations in a single cell is responsible for the altered growth state seen in these transformed epithelial cells.

RAR beta 2-mediated growth inhibition in HeLa cells

Retinoic acid inhibits the growth of a variety of normal and transformed cells in vitro and in vivo. How retinoic acid inhibits cell growth is poorly understood but involves interactions between the ligand and a series of nuclear and cytoplasmic receptors. The nuclear receptors for retinoic acid are of two types, the RARs and the RXRs. Each can function as a ligand-inducible transcription enhancing factor. In previous studies, we have demonstrated that an isoform of one RAR, RAR beta 2, is transcriptionally up-regulated in senescent human dermal fibroblasts and senescent human mammary epithelial cells. Moreover, we have also shown that RAR beta 2 can inhibit oncogene-induced focus formation, in primary rat embryo fibroblasts, as effectively as the tumor suppressor gene p53. Here, we extend our studies of retinoid-regulated signal transduction pathways that inhibit cell proliferation by demonstrating that HeLa cells expressing an RAR beta 2 construct are growth inhibited by greater than 50% when compared to the parent cell lines. The RAR beta 2-expressing cell lines are inhibited further by the addition of exogenous all-trans-retinoic acid. Finally, soft agar assays show that the RAR beta 2-expressing cell lines also demonstrate an inhibition of growth in soft agar, when compared to the parent growth cell lines, and are inhibited further in the presence of added all-trans-retinoic acid. These data definitively show that RAR beta 2 can inhibit cell proliferation in an established tumor cell line and provide more strength to the notion that this isoform is an effective growth inhibitor in vitro and, most likely, in vivo.

Effect of cellular senescence and retinoic acid on the expression of cellular retinoic acid binding proteins in skin fibroblasts

Retinoic acid (RA) has significant effects on a variety of cellular processes, including growth and differentiation. Retinoic acid has also been implicated as a major morphogen during embryogenesis. In the skin, both the epidermis and the dermis are extremely responsive to the effects of retinoids; however, the molecular mechanisms through which retinoids act in this tissue remain poorly understood. Two classes of proteins play roles in mediating the biological effects of retinoic acid. The nuclear receptors for retinoic acid are of two types, the initially described RARs, and the RXRs. Each of these nuclear receptor families has multiple isoforms and can function as a ligand-inducible transcription enhancing factor. A second class of receptor proteins exists for retinoic acid that are found in the cytoplasm, the cellular retinoic acid binding proteins (CRABPs). These proteins play a role in the binding, transport, and metabolism of retinoic acid. In previous studies, we have demonstrated that retinoic acid induces the expression of RAR beta and RAR gamma in human dermal fibroblasts. Moreover, we have also shown the selective transcriptional up-regulation of the RAR beta 2 isoform in senescent dermal fibroblasts and senescent human mammary epithelial cells. In order to further define molecules important in regulating the response of senescent dermal fibroblasts to retinoids, we demonstrate here that retinoic acid induces CRABP-II messenger RNA in human dermal fibroblasts in a dose-dependent manner. Moreover, we show that the induction by RA can be inhibited by actinomycin D, suggesting that the up-regulation may be mediated by a transcriptional mechanism. We further demonstrate that cycloheximide also has an effect on the up-regulation, suggesting a role for protein synthesis in the regulation of CRABP-II gene expression. We show that CRABP-II is a very stable messenger RNA species, in contrast to the mRNAs for RAR alpha, RAR beta, and RAR gamma. Of interest, we demonstrate no significant difference in the expression of CRABP-II between presenescent and senescent fibroblasts. Taken together, these data suggest that retinoic acid plays a central role in the regulation of CRABP-II gene expression in the dermal fibroblast and that this molecule is the major mediator of the cytoplasmic effects of retinoids in dermal fibroblasts. However, in contrast to RAR beta 2, there is no apparent change in the regulation of CRABP-II in senescent dermal fibroblasts.

Cellular aging and transformation suppression: a role for retinoic acid receptor beta 2

Cellular senescence is characterized by a finite proliferative capacity in vitro. Moreover, the proliferative capacity of dermal fibroblasts harvested from humans is inversely proportional to the age of the donor, suggesting that senescence in culture is a manifestation, at the cellular level, of processes that occur during in vivo human aging. As cellular senescence is a program that ultimately decreases cell proliferation, it has been hypothesized that the genetic mechanisms responsible for the negative growth regulation of senescence may also be involved in the suppression of neoplastic transformation. Retinoic acid (RA) and its derivatives are effective negative growth regulators and are known to inhibit tumor growth, in vitro and in vivo. As a first step in examining a role for retinoic acid in the regulation of cellular aging in human fibroblasts, we examined the expression of the nuclear receptors for RA (RAR alpha, RAR beta, and RAR gamma) in human donors of different ages. These studies demonstrate a selective up-regulation of RAR beta, in response to RA, in fibroblasts that manifest a decreased proliferative capacity. We extend these observations to show that this finding is independent of the age of the donor and correlates with the proliferative capacity of the culture as a whole. Nuclear run-on studies show that the increase in RAR beta mRNA accumulation is mediated by a striking increase in the transcription of the RAR beta 2 isoform. Senescent fibroblasts manifesting the transcriptional increase of the RAR beta 2 isoform also demonstrate transcriptional repression of the protooncogene, c-fos. Functional studies demonstrate that RAR beta 2, like the tumor suppressor gene p53, can inhibit oncogene-induced focus formation. These data provide further support for the contention that genetic events important in cellular senescence may also play a significant role in tumor suppression in humans. Moreover, these observations suggest that RA, through transcriptional regulation of RAR beta 2, may mediate aspects of the negative growth control that characterizes both states.

A beta 2RARE-LacZ transgene identifies retinoic acid-mediated transcriptional activation in distinct cutaneous sites

Retinoic acid and its derivatives (retinoids) exert profound influences on epithelial growth differentiation in a variety of tissues, including the skin. How retinoic acid mediates these effects is not fully understood. The recent cloning of a series of nuclear receptors for retinoic acid (RARs) has demonstrated that these proteins can function as ligand-inducible transcriptional enhancing factors. Moreover, all receptors are members of the steroid/thyroid hormone multigene family. In vitro studies have demonstrated the expression of RAR alpha, RAR beta, and RAR gamma in various cell types found in the skin. While multiple isoforms exist for each of the three RARs, it is unclear where each of these receptors functions in vivo to mediate the tissue-specific effects of retinoic acid. As a first step in determining sites of retinoic acid-mediated transcriptional activation in the skin and its appendages, we developed a transgenic model in which the retinoic acid response element (RARE) of the RAR beta 2 isoform is linked to a beta-galactosidase reporter gene. Our observations consistently demonstrate that retinoic acid transcriptionally activates the beta 2RARE in distinct areas of the skin. Of interest, certain of these areas are known to contain stem cells. These data clearly demonstrate that this type of transgenic "reporter" model can be used to further define retinoic acid-regulated signal transduction pathways in the skin, as well as other complex tissues. Furthermore, these observations raise the possibility that transcriptional activation of RAR beta 2 may regulate the growth and differentiation programs of selected populations of stem cells in the skin and its appendages.

Regulation of retinoic acid receptor expression in dermal fibroblasts

Retinoic acid (RA) is known to exert profound effects on growth and differentiation in a variety of cell types in the skin. In vitro studies have also shown that RA modulates gene expression in both fibroblasts and keratinocytes. Recently, three nuclear receptors specific for retinoic acid (RAR alpha, RAR beta, and RAR gamma) have been cloned and all are members of a large multigene family of ligand-inducible transcription enhancer factors. As a first step in defining the role of each receptor in the retinoid response of the skin, we examined the regulation of RAR alpha, RAR beta, and RAR gamma gene expression in human dermal fibroblasts by all-trans-retinoic acid. We demonstrate that human dermal fibroblasts express modest basal levels of RAR alpha and RAR gamma, but not RAR beta. When treated with 1 microM RA, the messenger RNAs for both RAR beta and RAR gamma are induced. In contrast, RAR alpha remains unchanged. The induction of RAR gamma is attenuated by the protein synthesis inhibitor, cycloheximide, while the induction of RAR beta increases slightly. Studies with actinomycin D and cycloheximide show that all three receptors have different half-lives, with RAR gamma having the longest half-life at 8 h. Gel shift analysis of known retinoic acid response elements (RAREs) in the RAR beta and RAR gamma genes demonstrates that the upregulation of these by genes by RA involves increased binding of complexes to the individual RAREs. In summary, these data demonstrate that fibroblasts express all three receptor types. Moreover, striking differences exist in the regulation of RAR gene expression in skin-derived fibroblasts and suggest that each receptor may well have a separate and discrete function in the retinoid response of the skin.

Down-regulation of retinoic acid receptor beta in mammary carcinoma cell lines and its up-regulation in senescing normal mammary epithelial cells

Retinoids are important cellular, dietary factors that regulate differentiation and cellular growth. They serve as ligands for specific nuclear receptors, the retinoic acid receptors (RARs). Ligand-activated receptors regulate gene transcription through target retinoic acid-responsive elements (RAREs) found in promoter regions. We have investigated the expression of retinoic acid receptor genes (alpha, beta, gamma) and retinoid X receptor beta in normal, senescing, and tumorigenic human mammary epithelial cells. We find that most tumor cells show a loss of RAR-beta expression, but that RAR-alpha and -gamma as well as retinoid X receptor beta are variably expressed in both normal and tumor cells. RAR-beta gene expression is induced both by retinoic acid and by fenretinide in normal cells, but tumor cells fail to respond to either. In contrast, RAR-beta expression increases with serial passage in senescing cells. Paradoxically, both normal and tumor cells can trans-activate an exogenous beta-RARE, as demonstrated by reporter gene assays. Oligonucleotide mobility shift assays with the beta-RARE show a single discrete complex in normal cells, whereas tumor cells exhibit a heterogeneous set of larger complexes, which indicates that tumor cells utilize a different array of factors within the beta-RARE. Reporter gene assays with extended promoter regions indicate the presence of negative regulatory elements and/or factor binding sites that reside between -1500 and the RARE located at -59, and that the promoter is down-regulated in MCF-7 tumor cells. Our findings reveal a dichotomy: RAR-beta transcription is down-regulated in tumor cells compared with normal human mammary epithelial cells, and up-regulated in senescence.

Cultured human melanocytes express the intermediate filament vimentin

Human melanocytes are neural crest-derived cells that synthesize the pigment melanin. These cells migrate from a central location to the dermal-epidermal junction early in gestation and situate themselves between keratinocytes of the basal layer of the epidermis, extending thin dendritic processes upwards into the epidermis. In vitro, neonatal melanocytes can assume a variety of morphologies, depending on the culture conditions. Using standard immunofluorescent, immunoblotting, and Northern blotting techniques, we investigated the expression of intermediate filament proteins and demonstrate here that cultured human melanocytes express vimentin gene and protein under a variety of culture conditions. Vimentin is a 57-kD intermediate filament protein synthesized primarily by cells of mesenchymal origin. It is transcribed as a single-messenger RNA species of 2.0 kb and the human gene is located on chromosome 10. As a member of the intermediate filament family of proteins, we suggest that vimentin is an important component of the cytoskeleton of neonatal, human melanocytes.

Clonal origin of dermatofibrosarcoma protuberans

Dermatofibrosarcoma protuberans (DFSP) is a malignant tumor originating in the dermis. Although it is known to be locally aggressive, it only rarely metastasizes and will recur unless completely excised. The exact cell responsible for the development of a DFSP has been a matter of controversy for several decades; however, most histochemical and electron microscopic studies support a fibroblastic origin, with the tumor cells staining uniformly for vimentin and containing active endoplasmic reticulum synthesizing collagen. Cytogenetic analysis of some of these tumors has demonstrated at least two specific chromosomal abnormalities in DFSP and suggested that this tumor may be polyclonal in origin. To further address the clonal origin of this locally invasive, mesenchymal tumor, we analyzed DNA from two female patients by restriction fragment length polymorphisms and methylation analysis. Our data strongly support the concept that DFSP is monoclonal in origin and that this tumor mass reflects the clonal expansion of a single cell.