Inactivation of p16 INK4a /CDKN2A gene may be a diagnostic feature of large B cell lymphoma leg type among cutaneous B cell lymphomas

Profiling of Copy Number Alterations Using Low-Coverage Whole-Genome Sequencing Informs Differential Diagnosis and Prognosis in Primary Cutaneous Follicle Center Lymphoma

Primary cutaneous follicle center lymphoma (PCFCL) has an excellent prognosis using local treatment, whereas nodal follicular lymphoma (nFL), occasionally presenting with cutaneous spread, often requires systemic therapy. Distinction of the 2 diseases based on histopathology alone might be challenging. Copy number alterations (CNAs) have scarcely been explored on a genome-wide scale in PCFCL; however, they might serve as potential biomarkers during differential diagnosis and risk stratification. Low-coverage whole-genome sequencing is a robust, high-throughput method for genome-wide copy number profiling. In this study, we analyzed 28 PCFCL samples from 20 patients and compared the copy number profiles with a cohort of diagnostic samples of 64 nFL patients. Although the copy number profile of PCFCL was similar to that of nFL, PCFCL lacked amplifications of 18q, with the frequency peaking at 18q21.33 in nFL cases involving the BCL2 locus (PCFCL: 5.0% vs nFL: 31.3%, P = .018, Fisher exact test). Development of distant cutaneous spread was significantly associated with higher genomic instability including the proportion of genome altered (0.02 vs 0.13, P = .033) and number of CNAs (2 vs 9 P = .017), as well as the enrichment of 2p22.2-p15 amplification involving REL and XPO1 (6.3% vs 60.0%, P = .005), 3q23-q24 amplification (0.0% vs 50.0%, P = .004), 6q16.1-q23.3 deletion (6.3% vs 50.0%, P = .018), and 9p21.3 deletion covering CDKN2A and CDKN2B loci (0.0% vs 40.0%, P = .014, all Fisher exact test) in PCFCL. Analysis of sequential tumor samples in 2 cases harboring an unfavorable clinical course pointed to the acquisition of 2p amplification in the earliest common progenitor underlining its pivotal role in malignant transformation. By performing genome-wide copy number profiling on the largest patient cohort to date, we identified distinctive CNA alterations conceivably facilitating the differential diagnosis of PCFCL and secondary cutaneous involvement of nFL and potentially aiding the risk stratification of patients with PCFCL in the future.

The molecular landscape and other distinctive features of primary cutaneous follicle center lymphoma

Primary cutaneous follicle center lymphoma (PCFCL) is distinguished from other follicular lymphomas (FLs) based on its clinicopathologic features including diminished CD10 and frequent lack of BCL2 rearrangements (R). Whether newer germinal center-associated markers would also be less commonly expressed and whether mutational studies would support its segregation from classic FL and FL subsets, including those which also typically lack BCL2R, are uncertain. To address these questions, 22 PCFCLs were stained for myocyte enhancer factor 2B (MEF2B) and human germinal center-associated lymphoma (HGAL), and targeted next-generation sequencing was performed with results compared to a meta-analysis of FL, pediatric-type FL (PTFL), low stage FL (LSFL) and other FL subsets. Selected fluorescence in situ hybridization studies were also performed. Although 27% of cases lacked CD10, all tested were MEF2B+ and HGAL+. The most common somatic mutations in the 12 to 19 analyzable PCFCL were TNFRSF14 (40%, plus 10% with 1p36 deletions), followed by CREBBP, TNFAIP3, KMT2D, SOCS1, EP300, STAT6, and FOXO1 (17-25%). Three of the most commonly mutated genes in FL (KMT2D, CREBBP, and BCL2) were significantly less commonly mutated in PCFCL than in FL, and TNFAIP was more commonly mutated with no difference for TNFRSF14 between PCFCL and FL or PTFL. CREBBP was also less frequently mutated than in LSFL but more frequently mutated than in PTFL. MAP2K1 mutations were much more common in PTFL (44% versus 0%). Two of 22 of the PCFCL had a BCL2 rearrangement and zero of 12 had a BCL6 rearrangement. These findings, while showing well-recognized and new shared features between PCFCL and other FL, highlight a distinctive mutational profile further supporting its recognition as a distinct entity.

Primary Cutaneous Follicle Center Lymphoma

CONTEXT.—

Primary cutaneous follicle center lymphoma is a low-grade B-cell lymphoma that is limited to the skin at diagnosis. It has a differential diagnosis that includes systemic/nodal follicular lymphoma secondarily involving the skin; primary cutaneous diffuse large B-cell lymphoma leg type; reactive lymphoid hyperplasia; and primary cutaneous marginal zone lymphoma.

OBJECTIVE.—

To review the clinical, morphologic, immunophenotypic, and genetic features of primary cutaneous follicle center lymphoma; its differential diagnosis; and the evidence that supports use of immunohistochemistry and genetic testing in the diagnosis and prognosis of this entity.

DATA SOURCES.—

Pertinent literature regarding cutaneous B-cell lymphomas is summarized and University of Michigan cases are used to highlight characteristics of primary cutaneous follicle center lymphoma.

CONCLUSIONS.—

Primary cutaneous follicle center lymphoma is a low-grade B-cell lymphoma with distinctive features, although some cases may have elements that overlap with other lymphomas, complicating interpretation.

[Diffuse large B-cell lymphoma with concomitant c-MYC and BCL6 gene rearrangements with primary skin involvement: A case report and a review of literature]

Double-hit lymphoma (DHL) is a rare aggressive B-cell lymphoma with concomitant c-MYC, BCL2 or BCL6 gene rearrangements, which is characterized by the high frequency of extranodal lesions and by resistance to chemotherapy. The median survival does not exceed 18 months in patients with this disease. The majority of DHL is represented by с-MYC/BCL2 cases. The combination of c-MYC/BCL6 occurs rarely (5-8%). The paper describes a case of DHL with concomitant c-MYC and BCL6 gene rearrangements, which mimics diffuse large B-cell lymphoma, leg-type.

Identification of Somatic Mutations in Primary Cutaneous Diffuse Large B-Cell Lymphoma, Leg Type by Massive Parallel Sequencing

To determine whether the mutational profile of primary cutaneous diffuse large B-cell lymphoma, leg type (PCLBCL-LT) is unique by comparison with other diffuse large B-cell lymphoma subtypes, we analyzed a total cohort of 20 PCLBCL-LT patients by using next-generation sequencing with a lymphoma panel designed for diffuse large B-cell lymphoma. We also analyzed 12 pairs of tumor and control DNA samples by whole-exome sequencing, which led us to perform resequencing of three selected genes not included in the lymphoma panel: TBL1XR1, KLHL6, and IKZF3. Our study clearly identifies an original mutational landscape of PCLBCL-LT with a very restricted set of highly recurrent mutations (>40%) involving MYD88 (p.L265P variant), PIM1, and CD79B. Other genes involved in B-cell signaling, NF-κB activation, or DNA modeling were found altered, notably TBL1XR1 (33%), MYC (26%) CREBBP (26%), and IRF4 (21%) or HIST1H1E (41%). MYD88^L265P variant was associated with copy number variations or copy neutral loss of heterozygosity in 60% of patients. The most frequent genetic losses involved CDKN2A/2B, TNFAIP3/A20, PRDM1, TCF3, and CIITA. Together, these results show that PCLBCL-LT exhibits a unique mutational landscape, combining highly recurrent hotspot mutations in genes involved in NF-kB and B-cell signaling pathways, which provides a rationale for using selective inhibitors of the B-cell receptor.

Cutaneous primary B-cell lymphomas: from diagnosis to treatment

Primary cutaneous B-cell lymphomas are a heterogeneous group of mature B-cells neoplasms with tropism for the skin, whose biology and clinical course differ significantly from the equivalent nodal lymphomas. The most indolent forms comprise the primary cutaneous marginal zone and follicle center B-cell lymphomas that despite the excellent prognosis have cutaneous recurrences very commonly. The most aggressive forms include the primary cutaneous large B-cell lymphomas, consisting in two major groups: the leg type, with poor prognosis, and others, the latter representing a heterogeneous group of lymphomas from which specific entities are supposed to be individualized over time, such as intravascular large B-cell lymphomas. Treatment may include surgical excision, radiotherapy, antibiotics, corticosteroids, interferon, monoclonal antibodies and chemotherapy, depending on the type of lymphoma and on the type and location of the skin lesions. In subtypes with good prognosis is contraindicated overtreatment and in those associated with a worse prognosis the recommended therapy relies on CHOP-like regimens associated with rituximab, assisted or not with local radiotherapy. We review the primary cutaneous B-cell lymphomas, remembering the diagnostic criteria, differential diagnosis, classification, and prognostic factors and presenting the available therapies.

Cutaneous lymphomas: an update. Part 2: B-cell lymphomas and related conditions

: Primary cutaneous B-cell lymphomas (PCBCL) are the second most common form of primary cutaneous lymphomas and account for approximately 25%-30% of all primary cutaneous lymphomas. Both forms of low-grade malignant PCBCL, primary cutaneous follicle center lymphoma (PCFCL) and primary cutaneous marginal zone lymphoma of mucosa-associated lymphoid tissue-type (MALT lymphoma) (PCMZL) represent the vast majority of PCBCL and show an indolent slowly progressive course and an excellent prognosis despite a high recurrence rate. Genetic analysis indicates that PCMZL differ from other forms of extranodal MALT lymphomas. The more common class-switched and the non-class-switched form of PCMZL can be distinguished as two distinctive subsets that differ in the cellular composition, IgM expression, and biological behavior with extracutaneous involvement found in the non-class-switched form. Recently, unusual clinical and histological forms of PCMZL and PCFCL manifesting with miliary or agminated lesions have been described that are diagnostically challenging. In contrast to PCMZL and PCFCL, primary cutaneous diffuse large B-cell lymphoma, leg type, and other rare forms of large B-cell lymphomas such as intravascular large B-cell lymphoma have an unfavorable prognosis. There is an emerging group of Epstein-Barr virus (EBV)-driven B-cell lymphoproliferations including posttransplant lymphoproliferative disorders and mucocutaneous ulcer occurring in immunocompromised patients and EBV-associated diffuse large B-cell lymphoma of the elderly arising in the setting of senescence-linked immunodeficiency. This review reports on recent findings expanding the spectrum of clinicopathological features, differential diagnostic aspects, and the pathogenesis of PCBCL and discusses the group of EBV-associated B-cell lymphoproliferations involving the skin.

Multiple genetic alterations in primary cutaneous large B-cell lymphoma, leg type support a common lymphomagenesis with activated B-cell-like diffuse large B-cell lymphoma

Primary cutaneous large B-cell lymphoma, leg type has been individualized from nodal diffuse large B-cell lymphoma. The objective of this study was to screen primary cutaneous large B-cell lymphoma, leg type for genetic alterations recently described in nodal diffuse large B-cell lymphoma. Skin biopsies from 23 patients were analyzed for IRF4, BCL2, BCL6, and MYC expression. FISH testing was performed for BCL2, BCL6, MYC with separation probes and for CDKN2A and PRDM1/BLIMP1 deletion. Multiple sequential FISH analyses with up to six probes were performed to define samples with multiple cytogenetic alterations. MYD88 mutations were studied by Sanger sequencing. All cases but one displayed at least one genetic alteration (96%). Nine patients exhibited a single genetic mutation and 12 combined several alterations (52%). We observed a split for BCL2, BCL6, or MYC in 1/23, 6/23, and 3/23 of cases, respectively. No double-hit lymphoma was observed. CDKN2A deletion was detected by FISH in only 5/23 cases. BLIMP1 and/or 6q deletion was observed at a higher rate in 10/20 of cases. No correlation between rearrangement and immunohistochemical expression was found for BCL2 or MYC. FISH tracking of sequential hybridizations showed that several alterations were carried by the same nuclei. The p.L265P MYD88 mutation was found in 11/18 (61%) of cases. Contrary to most cutaneous lymphomas that rarely harbor primary genetic alteration of their nodal histological equivalent, primary cutaneous large B-cell lymphoma, leg type seems to be a 'cutaneous counterpart' of activated B-cell-like diffuse large B-cell lymphoma with a similar cytogenetic profile and a high rate of MYD88 oncogenic L265P mutation. This also suggests a common lymphomagenesis with NF-κB activation, strong IRF4 expression and terminal B-cell differentiation blockage. Our data support the use of therapies targeting NF-κB, as most patients displayed disease progression and resistance to conventional therapies.

Cutaneous B-cell lymphoproliferative disorders: report of the 2011 Society for Hematopathology/European Association for Haematopathology workshop

The diagnosis and classification of the cutaneous B-cell lymphomas can be quite a challenge, with a definitive diagnosis sometimes being elusive, even when an extensive workup has been performed. Distinction of benign from neoplastic disorders can be difficult, with some hyperplasias mimicking lymphomas and vice versa. There are only a limited number of skin-specific B-cell lymphomas, including primary cutaneous follicle center lymphoma and primary cutaneous diffuse large B-cell lymphoma, leg type. Cutaneous marginal zone lymphomas have distinctive features but are classified with the other mucosa-associated lymphoid tissue lymphomas. It is important, however, to also remember that many other B-cell lymphomas/ plasma cell neoplasms can primarily, or more often secondarily, involve the skin. Some may mimic one of the skin-specific lymphomas but have very different clinical implications. Iatrogenic and senescent immunodeficiency-associated lymphoproliferative disorders that are often Epstein-Barr virus (EBV) positive can also primarily involve the skin, including cases also known as EBV-positive mucocutaneous ulcer.

The role of molecular pathology in the diagnosis of cutaneous lymphomas

Primary cutaneous lymphomas can be difficult to be distinguished from reactive mimics, even when integrating histologic, immunophenotypic, and clinical findings. Molecular studies, especially PCR-based antigen receptor gene rearrangement (ARGR) analysis, are frequently useful ancillary studies in the evaluation of cutaneous lymphoproliferations. The biologic basis of ARGR studies is discussed, as well as a comparison of various current protocols. The pitfalls and limitations of ARGR analysis are also highlighted. Recent advances in the understanding of the molecular pathogenesis of various cutaneous lymphomas are discussed. Some of these nascent discoveries may lead to the development of diagnostically useful molecular assays.

The collagen prolyl hydroxylases are novel transcriptionally silenced genes in lymphoma

BACKGROUND

Prolyl hydroxylation is a post-translational modification that affects the structure, stability and function of proteins including collagen by catalysing hydroxylation of proline to hydroxyproline through action of collagen prolyl hydroxylases3 (C-P3H) and 4 (C-P4H). Three C-P3Hs (nomenclature was amended according to approval by the HGNC symbols and names at http://www.genenames.org/ and Entrez database at http://www.ncbi.nlm.nih.gov/gene) leucineproline-enriched proteoglycan (leprecan) 1 (Lepre1), leprecan-like 1 (Leprel1), leprecan-like 2 (Leprel2) and two paralogs Cartilage-Related Protein (CRTAP) and leprecan-like 4 (Leprel4) are found in humans. The C-P4Hs are tetrameric proteins comprising a variable α subunit, encoded by the P4HA1, P4HA2 and P4HA3 genes and a constant β subunit encoded by P4HB.

METHODS

We used RT-PCR, qPCR, pyrosequencing, methylation-specific PCR, western blotting and immunohistochemistry to investigate expression and regulation of the C-P3H and C-P4H genes in B lymphomas and normal bone marrow.

RESULTS

C-P3H and C-P4H are downregulated in lymphoma. Down-regulation is associated with methylation in the CpG islands and is detected in almost all common types of B-cell lymphoma, but the CpG islands are unmethylated or methylated at lower levels in DNA isolated from normal bone marrow and lymphoblastoid cell lines. Methylation of multiple C-P3H and C-P4H genes is present in some lymphomas, particularly Burkitt's lymphoma.

CONCLUSIONS

Methylation of C-P3H and C-P4H is common in B lymphomas and may have utility in differentiating disease subtypes.

Genomic profiling using array comparative genomic hybridization define distinct subtypes of diffuse large B-cell lymphoma: a review of the literature

Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin Lymphoma comprising of greater than 30% of adult non-Hodgkin Lymphomas. DLBCL represents a diverse set of lymphomas, defined as diffuse proliferation of large B lymphoid cells. Numerous cytogenetic studies including karyotypes and fluorescent in situ hybridization (FISH), as well as morphological, biological, clinical, microarray and sequencing technologies have attempted to categorize DLBCL into morphological variants, molecular and immunophenotypic subgroups, as well as distinct disease entities. Despite such efforts, most lymphoma remains undistinguishable and falls into DLBCL, not otherwise specified (DLBCL-NOS). The advent of microarray-based studies (chromosome, RNA, gene expression, etc) has provided a plethora of high-resolution data that could potentially facilitate the finer classification of DLBCL. This review covers the microarray data currently published for DLBCL. We will focus on these types of data; 1) array based CGH; 2) classical CGH; and 3) gene expression profiling studies. The aims of this review were three-fold: (1) to catalog chromosome loci that are present in at least 20% or more of distinct DLBCL subtypes; a detailed list of gains and losses for different subtypes was generated in a table form to illustrate specific chromosome loci affected in selected subtypes; (2) to determine common and distinct copy number alterations among the different subtypes and based on this information, characteristic and similar chromosome loci for the different subtypes were depicted in two separate chromosome ideograms; and, (3) to list re-classified subtypes and those that remained indistinguishable after review of the microarray data. To the best of our knowledge, this is the first effort to compile and review available literatures on microarray analysis data and their practical utility in classifying DLBCL subtypes.

Although conventional cytogenetic methods such as Karyotypes and FISH have played a major role in classification schemes of lymphomas, better classification models are clearly needed to further understanding the biology, disease outcome and therapeutic management of DLBCL. In summary, microarray data reviewed here can provide better subtype specific classifications models for DLBCL.

High resolution array comparative genomic hybridization identifies copy number alterations in diffuse large B-cell lymphoma that predict response to immuno-chemotherapy

Despite recent attempts at sub-categorization, including gene expression profiling into prognostically different groups of "germinal center B-cell type" and "activated B-cell type," diffuse large B-cell lymphoma (DLBCL) remains a biologically heterogenous tumor with no clear prognostic biomarkers to guide therapy. Whole genome, high resolution array comparative genomic hybridization (aCGH) was performed on four cases of chemoresistant DLBCL and four cases of chemo-responsive DLBCL to identify genetic differences that may correlate with response to rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) therapy. Array CGH analysis identified seven DNA copy number alteration (CNA) regions exclusive to the chemoresistant group, consisting of amplifications at 1p36.13, 1q42.3, 3p21.31, 7q11.23, and 16p13.3, as well as loss at 9p21.3 and 14p21.31. Copy number loss of the tumor suppressor genes CDKN2A (p16, p14) and CDKN2B (p15) at 9p21.3 was validated by fluorescence in situ hybridization and immunohistochemistry as independent techniques. In the chemo-sensitive group, 12 CNAs were detected consisting of segment gains on 1p36.11, 1p36.22, 2q11.2, 8q24.3, 12p13.33, and 22q13.2, as well as segment loss on 6p21.32. RUNX3, a tumor suppressor gene located on 1p36.11 and MTHFR, which encodes for the enzyme methylenetetrahydrofolate reductase, located on 1p36.22, are the only known genes in this group associated with lymphoma. Whole genome aCGH analysis has detected copy number alterations exclusive to either chemoresistant or chemoresponsive DLBCL that may represent consistent clonal changes predictive for prognosis and outcome of chemotherapy.

Simultaneous aberrations of single CDKN2A network components and a high Rb phosphorylation status can differentiate subgroups of primary cutaneous B-cell lymphomas

The cyclin-dependent kinase inhibitor 2A (CDKN2A) gene on chromosome 9p21 encodes p16 (INK4A), the inhibitor of the CDK4/retinoblastoma (Rb) cell proliferation pathway, as well as p14 (ARF), which controls p53-dependent pathways. Inactivation of p16 has previously been associated with the prognostically unfavourable primary cutaneous diffuse large B-cell lymphoma, leg type (PCLBCL, LT). In this work, we analysed 22 tumors [nine primary cutaneous follicle centre lymphomas (PCFCL), seven primary cutaneous marginal zone lymphomas (PCMZL) and six PCLBCL, LT] not only for alterations of the p16 gene but also for p14, p53 and Rb by fluorescence in situ hybridization (FISH) and immunohistochemistry. In most PCLBCL, LT (4/6) alterations of CDKN2A (two biallelic deletions, one monoallelic deletion and one trisomy 9) and in addition the highest frequency of deletions of p53 (3/6) and Rb (3/6) were detected. p16 was not expressed but very high levels of phosphorylated Rb, indicating a functional effect of genomic CDKN2A alterations on the protein level in PCLBCL, LT. Regarding the p14/p53 axis, PCLBCL, LT showed a variable expression. Neither PCFCL nor PCMZL showed alterations of CDKN2A and also deletions of p53 or Rb were extremely rare in these subtypes. Exclusively in PCMZL, p53 protein was consistently lacking. In conclusion, only PCLBCL, LT is characterized by a high frequency of aberrations of the CDKN2A network components in both important tumor suppressor pathways regulated by the CDKN2A gene. Moreover, PCLBCL, LT appears to be distinguishable from PCMZL not only by its level of p53 expression but also by its stage of Rb phosphorylation. The latter may also apply to a subgroup of PCFCL.

Primary cutaneous diffuse large B-cell lymphoma, leg-type, treated with a modified R-CHOP immunochemotherapy - diagnostic and therapeutic challenges

BACKGROUND

Primary cutaneous diffuse large B-cell lymphoma (PCLBCL) represents a rare subtype among primary cutaneous B-cell lymphoma exhibiting a characteristic genetic background, an aggressive clinical course and a high relapse rate under different therapeutic regimen. Therefore, PCLBCL has a rather restricted prognosis.

PATIENTS AND METHODS

Four patients with PCLBCL were treated at our institution with age- and toxicity-adapted first-line immunochemotherapy with rituximab and modified CHOP (cyclophosphamid, vincristin, liposomal doxorubicin, prednisolon). On relapse, the same regimen with R-CHOP or different antineoplastic strategies (radiation, polychemotherapy, immunotherapy, stem cell transplantation) were applied. Toxicity, clinical response and overall survival was documented.

RESULTS

Under this regimen, clinical response to modified R-CHOP was achieved in all patients with tolerable toxicity - however, being characterized by a rapid disease progression with inconsistent response towards the subsequent therapeutic armentarium and unsecure impact on overall survival.

CONCLUSIONS

So far, it is still unknown, if an extensive multimodal therapy for PBLBCL improves overall survival. Immunochemotherapy with R-CHOP currently represents the most effective treatment.

CDKN2A-CDKN2B deletion defines an aggressive subset of cutaneous T-cell lymphoma

Inactivation of the CDKN2A-CDKN2B locus has been reported in the most frequent subtypes of cutaneous T-cell lymphomas (CTCLs), mycosis fungoides, Sézary syndrome (SS) and CD30+ cutaneous anaplastic large cell lymphoma. To investigate whether genetic or epigenetic inactivation of CDKN2A-CDKN2B is more specifically observed in certain CTCL subtypes with clinical impact, we used array-comparative genomic hybridization, quantitative PCR, interphase fluorescent in situ hybridization and methylation analyses of p14(ARF) p16(INK4A) and p15(INK4B) promoters. We studied 67 samples from 58 patients with either transformed mycosis fungoides (n=24), SS (n=16) or CD30+ cutaneous anaplastic large cell lymphoma (n=18). We observed combined CDKN2A-CDKN2B deletion in both transformed mycosis fungoides (n=17, 71%) and SS patients (n=7, 44%), but, surprisingly, in only one CD30+ cutaneous anaplastic large cell lymphoma case. Interphase fluorescent in situ hybridization showed 9p21 loss in 17 out of 19 cases, with 9p21 deletion indicating either hemizygous (n=4) or homozygous (n=2) deletion, with mixed patterns in most patients (n=11). The limited size of 9p21 deletion was found to account for false-negative detection by either BAC arrays (n=9) or fluorescent in situ hybridization (n=2), especially in patients with Sézary syndrome (n=6). Methylation was found to be restricted to the p15(INK4B) gene promoter in patients with or without 9p21 deletion and did not correlate with prognosis. In contrast, CDKN2A-CDKN2B genetic loss was strongly associated with a shorter survival in CTCL patients (P=0.002) and more specifically at 24 months in transformed mycosis fungoides and SS patients (P=0.02). As immunohistochemistry for p16(INK4A) protein was not found to be informative, the genetic status of the CDKN2A-CDKN2B locus would be relevant in assessing patients with epidermotropic CTCLs in order to identify those cases where the disease was more aggressive.

Aberrant DNA methylation in skin diseases

Epigenetic mechanisms are involved in regulating cell growth and differentiation without inducing changes in the gene sequence. The main epigenetic mechanisms include DNA methylation, histone modification, and microRNA. Recent studies indicate that aberrant DNA methylation is a common feature of many human disorders, including cancer, autoimmune diseases, heart diseases, skin diseases, and others. Skin diseases comprise various diseases that have a complex etiology and pathogenesis, including genetics and acquired factors such as environment and diet. These acquired factors often have pathogenic effects through modification of DNA and histones, of which DNA methylation is the most common mechanism. Aberrant DNA methylation has been demonstrated in skin diseases, including skin tumors and autoimmune-related skin disorders. Herein, we review the role of DNA methylation in the pathogenesis of skin diseases.

CARF: an emerging regulator of p53 tumor suppressor and senescence pathway

Replicative senescence, a major outcome of normal cells with finite lifespan, is a widely accepted in vitro model for ageing studies. Limited repair and defense mechanisms of normal cells, in addition to DNA alterations and oncogene inductions under stress, are believed to result in senescence as a protective mechanism to prevent undesirable proliferation of cells. The ARF/p53/p21(cip1/waf1) tumor suppression pathway acts as a molecular sensor and regulator of cellular stress, senescence, and immortalization. Understanding the molecular regulation of this pathway by intrinsic and extrinsic signals is extremely important to address unsolved questions in senescence and cancer. CARF was first discovered as a binding partner of ARF and has since been shown to have both ARF-dependent and -independent functions that converge to regulate p53 pathway. CARF directly binds to p53 and HDM2, and functions in a negative feedback pathway. Whereas CARF transcriptionally represses HDM2 to increase p53 activity, HDM2 in return degrades CARF. Thus, CARF may act as a novel key regulator of the p53 pathway at multiple checkpoints. The aim of this article is to discuss the current knowledge about functions of CARF and its impact on p53 pathway in regulation of senescence and carcinogenesis.