A novel gene expressed in human keratinocytes with long-term in vitro growth potential is required for cell growth

Isolation of an "Early" Transit Amplifying Keratinocyte Population in Human Epidermis: A Role for the Low Affinity Neurotrophin Receptor CD271

In the interfollicular epidermis (IFE), stem cells (KSC) generate transit amplifying (TA) cells that, after symmetric divisions, produce differentiating daughters. Here, we isolated and characterized the highly proliferative interfollicular epidermal basal cell population "early" TA (ETA) cells, based on their capacity to adhere to type IV collagen. Proliferation and colony-forming efficiency in ETA cells are lower than in KSC but higher than in "late" TA (LTA). Stemness, proliferation, and differentiation markers confirmed that ETA cells display a unique phenotype. Skin reconstructs derived from ETA cells present different features (epidermal thickness, Ki67, and Survivin expression), as compared to skin equivalents generated from either KSC or LTA cells. The low-affinity neurotrophin receptor CD271, which regulates the KSC to TA cell transition in the human epidermis through an on/off switch control mechanism, is predominantly expressed in ETA cells. Skin equivalents generated from siRNA CD271 ETA cells display a more proliferative and less differentiated phenotype, as compared to mock-derived reconstructs. Consistently, CD271 overexpression in LTA cells generates a more proliferative skin equivalent than mock LTA cells. Finally, the CD271 level declines with cellular senescence, while it induces a delay in p16INK4 expression. We conclude that ETA cells represent the first KSC progenitor with exclusive features. CD271 identifies and modulates ETA cells, thus participating in the early differentiation and regenerative capacity of the human epidermis.

H11/HspB8 and Its Herpes Simplex Virus Type 2 Homologue ICP10PK Share Functions That Regulate Cell Life/Death Decisions and Human Disease

Small heat shock proteins (sHsp) also known as HspB are a large family of widely expressed proteins that contain a 90 residues domain known as α-crystallin. Here, we focus on the family member H11/HspB8 and its herpes simplex virus type 2 (HSV-2) homologue ICP10PK, and discuss the possible impact of this relationship on human disease. H11/HspB8 and ICP10PK are atypical protein kinases. They share multi-functional activity that encompasses signaling, unfolded protein response (UPR) and the regulation of life cycle potential. In melanocytes H11/HspB8 causes growth arrest. It is silenced in a high proportion of melanoma prostate cancer, Ewing's sarcoma and hematologic malignancies through aberrant DNA methylation. Its restored expression induces cell death and inhibits tumor growth in xenograft models, identifying H11/HspB8 as a tumor suppressor. This function involves the activation of multiple and distinct death pathways, all of which initiate with H11/HspB8-mediated phosphorylation of transforming growth factor β-activated kinase 1 (TAK1). Both ICP10PK and H11/HspB8 were implicated in inflammatory processes that involve dendritic cells activation through Toll-like receptor-dependent pathways and may contribute to the onset of autoimmunity. The potential evolutionary relationship of H11/HspB8 to ICP10PK, its impact on human disorders and the development of therapeutic strategies are discussed.

Restored expression of the atypical heat shock protein H11/HspB8 inhibits the growth of genetically diverse melanoma tumors through activation of novel TAK1-dependent death pathways

Melanoma is an aggressive and drug-resistant cancer in need of improved therapeutic strategies. Restored expression of transcriptionally silenced genes is a potential approach, but it is limited by the genetic diversity of the melanoma tumors. The atypical heat shock protein H11/HspB8 has kinase activity and is silenced in melanoma through aberrant DNA methylation. We report that its restored expression induces the death of genetically diverse melanoma lines and inhibits tumor growth through the activation of novel TAK1-dependent death pathways. These include (i) caspase-1 activation independent of the inflammasome through upregulation of apoptosis-associated speck-like protein containing a CARD (ASC), (ii) Beclin-1 upregulation through phosphorylation of mammalian target of rapamycin (mTOR) at S2481 and (iii) apoptosis caused by caspase-1-mediated Beclin-1 cleavage. These data extend current understanding of cell death-associated functions, underscore the strong therapeutic promise of H11/HspB8 and identify TAK1 as a potential intervention target in melanoma.

HSPB8 is methylated in hematopoietic malignancies and overexpression of HSPB8 exhibits antileukemia effect

HSPB8 has been shown to be involved in regulation of cell proliferation and apoptosis, and it has also been found to have divergent properties in solid tumors. The purpose of this study was to investigate the expression and function of HSPB8 in hematopoietic malignancies. Expression and induced expression of HSPB8 was evaluated in hematopoietic tumor cell lines and bone marrow samples from patients with leukemia. Methylation status was investigated by methylation-specific polymerase chain reaction. The role of HSPB8 in hematopoietic malignancies was addressed by reintroducing HSPB8 expression into the K562 (leukemia) and Namalwa (lymphoma) cell lines. Expression of HSPB8 was absent in hematopoietic tumor cell lines and primary patient and normal volunteer samples. Promoter DNA methylation of HSPB8 was observed in these cells. HSPB8 expression could be restored after demethylation treatment with 5-aza-2'-deoxycytidine. Overexpression of HSPB8 reduced colony formation of both K562 and Namalwa cell lines, inhibited the cell growth of Namalwa in vitro, and suppressed tumor formation of K562 cells in vivo. The present study demonstrates that HSPB8 is silenced by DNA methylation in hematopoietic malignant and normal cells and its expression can be induced by treatment with 5-aza-2'-deoxycytidine. Overexpression of HSPB8 may have an antitumor activity in chronic myelogenous leukemia and lymphoma.

The Levels of H11/HspB8 DNA methylation in human melanoma tissues and xenografts are a critical molecular marker for 5-Aza-2'-deoxycytidine therapy

H11/HspB8 is a functionally distinct small heat shock protein. It causes growth arrest in melanocytes, associated with the inhibition of Cyclin E/Cdk2 and β-catenin phosphorylation at the transcriptional activity site Ser(552) and is silenced through DNA methylation in 27/35 (77%) melanoma tissues/early cultures. 5-Aza-2'-deoxycytidine (Aza-C) induces melanoma cell death correlated with the levels of H11/HspB8 DNA methylation (p < .001). In line with low/moderate H11/HspB8 methylation, PI3-K inhibition increases Aza-C-induced cell death. Aza-C inhibits the growth of melanoma xenografts related to the levels of H11/HspB8 methylation, and a nonmethylated/non-TAK1 binding H11/HspB8 mutant confers Aza-C resistance. H11/HspB8 is a potential molecular marker for demethylation therapies.

HSPB2/MKBP, a novel and unique member of the small heat-shock protein family

Although proteins belonging to the sHSP superfamily are diverse in sequence and size, most share characteristic features, including 1) a small molecular mass of 12-43 kDa, 2) a conserved alpha-crystallin domain of 80-100 residues, 3) formation of large oligomers, 4) a dynamic quaternary structure, and 5) induction by stress conditions and chaperone activity in suppressing protein aggregation. HSPB2/MKBP (myotonic dystrophy kinase-bind-protein) retains the structural motif of the alpha-crystallin family of HSPs but shows a unique nature compared with canonical family members, characterized by gene allocation, specific binding partners in skeletal muscle, and unique stress responsiveness. MKBP may be involved in the pathogenesis of myotonic dystrophy and contribute to the neuropathology in both Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis, Dutch type.

Structure, function, property, and role in neurologic diseases and other diseases of the sHsp22

Small heat shock proteins are members of the heat shock proteins family. They share important identical features: 1) they form the conserved structure 'alpha-crystallin domain' with about 80-100 residues in the C-terminal part of the proteins; 2) they have monomeric molecular masses ranging in 12-43 kDa; 3) they associate into large oligomers consisting in many cases of subunits; 4) they increase expression under stress conditions; 5) they exhibit a highly dynamic structure; and 6) they play a chaperone-like role. Hsp22 (also known as HspB8, H11, and E2IG1) retains the structural motif of the 'alpha-crystallin' family of Hsps and is a member of the superfamily of sHsps. Hsp22 displays chaperone activity, autokinase activity, and trigger or block apoptosis activity. It differs from canonical family members existing as a monomer. A decrease in the HspB8 activity may contribute to the development of some neurologic diseases and others.

Stress up-regulates neuronal expression of the herpes simplex virus type 2 large subunit of ribonucleotide reductase (R1; ICP10) by activating activator protein 1

Herpes simplex virus type 2 (HSV-2) genes expressed in neuronal cells in response to stress stimuli that trigger latency reactivation are largely unknown. Using a chloramphenicol acetyltransferase (CAT) reporter assay we found that stress caused a significant (P < .001) increase in ICP10 expression in neuronal cells. Up-regulation correlated with activator protein (AP)-1 activation, notably c-Jun and c-Fos that bind cognate elements in the ICP10 promoter. It was blocked by mutation of the AP-1 motifs in the ICP10 promoter. ICP10 expression protected neuronal cells from stress-induced apoptosis. The data suggest that ICP10 may contribute to HSV-2 reactivation by increasing neuronal survival.

CD34+ cells in the peripheral blood transport herpes simplex virus DNA fragments to the skin of patients with erythema multiforme (HAEM)

Herpes simplex virus (HSV)-associated erythema multiforme (HAEM) is a recurrent disease characterized by the presence and expression of HSV DNA fragments in lesional skin. Our studies examined the mechanism of viral DNA transport to the skin of HAEM patients. CD34+ cells were isolated from the blood of normal subjects and HSV and HAEM patients during acute lesions and at quiescence. They were cultured with cytokines that favor their differentiation into Langerhans cells (LC) precursors (CD1a+/CD14-) and examined for HSV replication, HSV-induced cellular alterations, viral DNA fragmentation, and clearance. CD34+ cells from all study groups were non-permissive for HSV replication but infection favored their differentiation into CD1a+/CD14- LC precursors and upregulated E-cadherin expression, thereby assisting LC targeting to the skin. Only HAEM patients had CD34+ cells that retained viral DNA fragments, notably polymerase DNA, for at least 7 d of in vitro culture. The percentages of circulating CD34+ (and CD34+/CLA+) cells were significantly higher in HAEM patients at the time of acute lesions. A similar increase was not seen for HSV patients. The data are the first report implicating CD34+ cells in HAEM pathogenesis, likely by transporting HSV DNA fragments to lesional skin.

Cellular process classification of human papillomavirus-16-positive SiHa cervical carcinoma cell using Gene Ontology

This study utilized mRNA differential display and the Gene Ontology (GO) analysis to characterize the multiple interactions of a number of genes involved in human papillomavirus (HPV)-16-induced cervical carcinogenesis. We used HPV-16-positive cervical cancer cell line (SiHa) and normal human keratinocyte cell line (HaCaT) as a control. Each gene has several biological functions in the GO, and hence, we chosen the several functions for each gene. and then, the specific functions were correlated with gene expression patterns. The results showed that 157 genes were up- or down-regulated above two-fold and organized into mutually dependent subfunction sets depending on the cervical cancer pathway, suggesting the potentially significant genes of unknown function. The GO analysis suggested that cervical cancer cells underwent repression of cancer-specific cell-adhesive properties. Also, genes belonging to DNA metabolism such as DNA repair and replication were strongly down-regulated, whereas significant increases were shown in protein degradation and in protein synthesis. The GO analysis can overcome the complexity of the gene expression profile of the HPV-16-associated pathway and identify several cancer-specific cellular processes as well as genes of unknown function. Also, it can become a major competing platform for the genome-wide characterization of carcinogenesis.

Interaction of Human HSP22 (HSPB8) with Other Small Heat Shock Proteins

Mammalian small heat shock proteins (sHSP) are abundant in muscles and are implicated in both muscle function and myopathies. Recently a new sHSP, HSP22 (HSPB8, H11), was identified in the human heart by its interaction with HSP27 (HSPB1). Using phylogenetic analysis we show that HSP22 is a true member of the sHSP superfamily. sHSPs interact with each other and form homo- and hetero-oligomeric complexes. The function of these complexes is poorly understood. Using gel filtration HPLC, the yeast two-hybrid method, immunoprecipitation, cross-linking, and fluorescence resonance energy transfer microscopy, we report that (i). HSP22 forms high molecular mass complexes in the heart, (ii). HSP22 interacts with itself, cvHSP (HSPB7), MKBP (HSPB2) and HSP27, and (iii). HSP22 has two binding domains (N- and C-terminal) that are specific for different binding partners. HSP22 homo-dimers are formed through N-N and N-C interactions, and HSP22-cvHSP hetero-dimers through C-C interaction. HSP22-MKBP and HSP22-HSP27 hetero-dimers involve the N and C termini of HSP22 and HSP27, respectively, but appear to require full-length protein as a binding partner.

Forced expression of the H11 heat shock protein can be regulated by DNA methylation and trigger apoptosis in human cells

H11, the eukaryotic homologue of a herpes simplex virus protein, has the crystallin motif of heat shock proteins (Hsp), but it differs from canonical family members in that mRNA and protein levels were reduced in various tumor tissues and cell lines (viz. melanoma, prostate cancer and sarcoma) relative to their normal counterparts. In these cells, expression was not restored by heat shock, but rather by the demethylating agent 5-aza-2'-deoxycytidine (Aza-C). Forced H11 expression by Aza-C treatment, transient transfection with H11 expression vectors, or retrovirus-mediated delivery of H11 under the control of a tetracycline-sensitive promoter triggered apoptosis. This is evidenced by a significant (p < 0.001) increase in the percentage of cells positive for terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL) and for activation of caspase-3 and p38MAPK and by the co-localization of TUNEL+ nuclei with increased H11 levels. Apoptosis was partially inhibited by the pancaspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone or the p38MAPK inhibitor SB203580. It was abrogated by co-treatment with both inhibitors, suggesting that H11-triggered apoptosis is both caspase- and p38MAPK-dependent. A single site mutant (H11-W51C) had cytoprotective activity related to MEK/ERK activation, and it blocked H11-induced apoptosis in co-transfected and Aza-C-treated cells, indicating that it is a dominant negative mutant. This is the first report of a heat shock protein with proapoptotic activity.

The sperm outer dense fiber protein is the 10th member of the superfamily of mammalian small stress proteins

Nine proteins have been assigned to date to the superfamily of mammalian small heat shock proteins (sHsps): Hsp27 (HspB1, Hsp25), myotonic dystrophy protein kinase-binding protein (MKBP) (HspB2), HspB3, alphaA-crystallin (HspB4), alphaB-crystallin (HspB5), Hsp20 (p20, HspB6), cardiovascular heat shock protein (cvHsp [HspB7]), Hsp22 (HspB8), and HspB9. The most pronounced structural feature of sHsps is the alpha-crystallin domain, a conserved stretch of approximately 80 amino acid residues in the C-terminal half of the molecule. Using the alpha-crystallin domain of human Hsp27 as query in a BLAST search, we found sequence similarity with another mammalian protein, the sperm outer dense fiber protein (ODFP). ODFP occurs exclusively in the axoneme of sperm cells. Multiple alignment of human ODFP with the other human sHsps reveals that the primary structure of ODFP fits into the sequence pattern that is typical for this protein superfamily: alpha-crystallin domain (conserved), N-terminal domain (less conserved), central region (variable), and C-terminal tails (variable). In a phylogenetic analysis of 167 proteins of the sHsp superfamily, using Bayesian inference, mammalian ODFPs form a clade and are nested within previously identified sHsps, some of which have been implicated in cytoskeletal functions. Both the multiple alignment and the phylogeny suggest that ODFP is the 10th member of the superfamily of mammalian sHsps, and we propose to name it HspB10 in analogy with the other sHsps. The C-terminal tail of HspB10 has a remarkable low-complexity structure consisting of 10 repeats of the motif C-X-P. A BLAST search using the C-terminal tail as query revealed similarity with sequence elements in a number of Drosophila male sperm proteins, and mammalian type I keratins and cornifin-alpha. Taken together, the following findings suggest a specialized role of HspB10 in cytoskeleton: (1) the exclusive location in sperm cell tails, (2) the phylogenetic relationship with sHsps implicated in cytoskeletal functions, and (3) the partial similarity with cytoskeletal proteins.

The herpes simplex virus type 2 R1 protein kinase (ICP10 PK) functions as a dominant regulator of apoptosis in hippocampal neurons involving activation of the ERK survival pathway and upregulation of the antiapoptotic protein Bag-1

Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) can trigger or block apoptosis in a cell type-dependent manner. We have recently shown that the protein kinase activity of the large subunit of the HSV-2 ribonucleotide reductase (R1) protein (ICP10 PK) blocks apoptosis in cultured hippocampal neurons by activating the extracellular signal-regulated kinase (ERK) survival pathway (Perkins et al., J. Virol. 76:1435-1449, 2002). The present studies were designed to better elucidate the mechanism of ICP10 PK-induced neuroprotection and determine whether HSV-1 has similar activity. The data indicate that apoptosis inhibition by ICP10 PK involves a c-Raf-1-dependent mechanism and induction of the antiapoptotic protein Bag-1 by the activated ERK survival pathway. Also associated with neuroprotection by ICP10 PK are increased activation/stability of the transcription factor CREB and stabilization of the antiapoptotic protein Bcl-2. HSV-1 and the ICP10 PK-deleted HSV-2 mutant ICP10DeltaPK activate JNK, c-Jun, and ATF-2, induce the proapoptotic protein BAD, and trigger apoptosis in hippocampal neurons. c-Jun activation and apoptosis are inhibited in hippocampal cultures infected with HSV-1 in the presence of the JNK inhibitor SP600125, suggesting that JNK/c-Jun activation is required for HSV-1-induced apoptosis. Ectopically delivered ICP10 PK (but not its PK-negative mutant p139) inhibits apoptosis triggered by HSV-1 or ICP10DeltaPK. Collectively, the data indicate that ICP10 PK-induced activation of the ERK survival pathway results in Bag-1 upregulation and overrides the proapoptotic JNK/c-Jun signal induced by other viral proteins.

Recent progress in herpes simplex virus immunobiology and vaccine research

Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) cause prevalent, chronic infections that have serious outcomes in some individuals. Neonatal herpes may occur when the infant traverses the cervix during maternal genital herpes. Genital herpes is a major risk factor for human immunodeficiency virus type 1 transmission. Considerable efforts have been made to design and test vaccines for HSV, focusing on genital infection with HSV-2. Several protein subunit vaccines based on HSV-2 envelope glycoproteins have reached advanced-phase clinical trials. These antigens were chosen because they are the targets of neutralizing-antibody responses and because they elicit cellular immunity. Encouraging results have been reported in studies of treatment of HSV-seronegative women with a vaccine consisting of truncated glycoprotein D of HSV-2 and a novel adjuvant. Because most sexual HSV transmission occurs during asymptomatic shedding, it is important to evaluate the impact of vaccination on HSV-2 infection, clinically apparent genital herpes, and HSV shedding among vaccine recipients who acquire infection. There are several other attractive formats, including subunit vaccines that target cellular immune responses, live attenuated virus strains, and mutant strains that undergo incomplete lytic replication. HSV vaccines have also been evaluated for the immunotherapy of established HSV infection.

Development of HSV-specific CD4+ Th1 responses and CD8+ cytotoxic T lymphocytes with antiviral activity by vaccination with the HSV-2 mutant ICP10DeltaPK

A growth compromised herpes simplex virus type 2 (HSV-2) mutant which is deleted in the PK domain of the large subunit of ribonucleotide reductase (ICP10DeltaPK) protects from HSV-2 challenge in the mouse and guinea pig cutaneous and vaginal models and reduces the incidence and frequency of recurrent disease (Vaccine (17) (1999) 1951; Vaccine (19) (2001) 1879). The present studies were designed to identify the immune responses induced by ICP10DeltaPK and define the component responsible for protective activity. We found that ICP10DeltaPK elicits a predominant HSV-specific T helper type 1 (Th1) response, as evidenced by: (1) higher levels of HSV-specific IgG2a (Th1) than IgG1 (Th2) isotypes and (2) higher numbers of CD4+ IFN-gamma than IL-10 secreting T cells in popliteal lymph nodes. This Th1 response pattern was associated with a significant increase in the levels of IL-12 produced by dendritic cells from ICP10DeltaPK than HSV-2 immunized animals. Lymph node cells (LNCs) from ICP10DeltaPK immunized mice had significantly higher levels of HSV-2 specific cytolytic activity than LNCs from mice immunized with HSV-2 and it was mediated by CD8+ T cells. CD8+ CTL were not seen in LNCs from HSV-2 immunized mice. In adoptive transfer experiments, CD8+ T cells and, to a lower extent, CD4+ T cells from ICP10DeltaPK immunized mice inhibited HSV-2 replication, suggesting that they are involved in the protective immunity induced by ICP10DeltaPK vaccination.

The herpes simplex virus type 2 R1 protein kinase (ICP10 PK) blocks apoptosis in hippocampal neurons, involving activation of the MEK/MAPK survival pathway

Herpes simplex virus type 1 (HSV-1) and HSV-2 trigger or counteract apoptosis by a cell-specific mechanism. Our studies are based on previous findings that the protein kinase (PK) domain of the large subunit of HSV-2 ribonucleotide reductase (ICP10) activates the Ras/MEK/MAPK pathway (Smith et al., J. Virol. 74:10417, 2000). Because survival pathways can modulate apoptosis, we used cells that are stably or transiently transfected with ICP10 PK, an HSV-2 mutant deleted in ICP10 PK (ICP10DeltaPK) and the MEK-specific inhibitor U0126 to examine the role of ICP10 PK in apoptosis. Apoptosis was induced by staurosporine or D-mannitol in human (HEK293) cells or HEK293 cells stably transfected with the ICP10 PK-negative mutant p139 (JHL15), as determined by morphology, DNA fragmentation, terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL), caspase-3 activation, and poly(ADP-ribose) polymerase (PARP) cleavage. HEK293 cells stably transfected with ICP10 (JHLa1) were protected from apoptosis. ICP10 but not p139 protected neuronally differentiated PC12 cells from death due to nerve growth factor withdrawal, and apoptosis (determined by TUNEL) and caspase-3 activation were seen in primary hippocampal cultures infected with ICP10DeltaPK but not with HSV-2 or a revertant virus [HSV-2(R)]. The data indicate that ICP10 has antiapoptotic activity under both paradigms and that it requires a functional PK activity. The apoptotic cells in primary hippocampal cultures were neurons, as determined by double immunofluorescence with fluorescein-labeled dUTP (TUNEL) and phycoerythrin-labeled antibodies specific for neuronal proteins (TuJ1 and NF-160). Protection from apoptosis was associated with MEK/MAPK activation, as evidenced by (i) increased levels of activated (phosphorylated) MAPK in HSV-2- but not ICP10DeltaPK-infected cultures and (ii) inhibition of MAPK activation by the MEK-specific inhibitor U0126. MEK and MAPK were activated by infection with UV-inactivated but not antibody-neutralized HSV-2, suggesting that activation requires cellular penetration but is independent of de novo viral protein synthesis.