Emily Y. Chu

Control of apoptosis and mitotic spindle checkpoint by survivin

Progression of the cell cycle and control of apoptosis (programmed cell death) are thought to be intimately linked processes, acting to preserve homeostasis and developmental morphogenesis. Although proteins that regulate apoptosis have been implicated in restraining cell-cycle entry and controlling ploidy (chromosome number), the effector molecules at the interface between cell proliferation and cell survival have remained elusive. Here we show that a new inhibitor of apoptosis (IAP) protein,, survivin, is expressed in the G2/M phase of the cell cycle in a cycle-regulated manner. At the beginning of mitosis, survivin associates with microtubules of the mitotic spindle in a specific and saturable reaction that is regulated by microtubule dynamics. Disruption of survivin–microtubule interactions results in loss of survivins anti-apoptosis function and increased caspase-3 activity, a mechanism involved in cell death, during mitosis. These results indicate that survivin may counteract a default induction of apoptosis in G2/M phase. The overexpression of survivin in cancer may overcome this apoptotic checkpoint and favour aberrant progression of transformed cells through mitosis.

Epithelial Bmpr1a regulates differentiation and proliferation in postnatal hair follicles and is essential for tooth development

Bone morphogenetic protein (BMP) signaling is thought to perform multiple functions in the regulation of skin appendage morphogenesis and the postnatal growth of hair follicles. However, definitive genetic evidence for these roles has been lacking. Here, we show that Cre-mediated mutation of the gene encoding BMP receptor 1A in the surface epithelium and its derivatives causes arrest of tooth morphogenesis and lack of external hair. The hair shaft and hair follicle inner root sheath (IRS) fail to differentiate, and expression of the known transcriptional regulators of follicular differentiation Msx1, Msx2, Foxn1 and Gata3 is markedly downregulated or absent in mutant follicles. Lef1 expression is maintained, but nuclearβ -catenin is absent from the epithelium of severely affected mutant follicles, indicating that activation of the WNT pathway lies downstream of BMPR1A signaling in postnatal follicles. Mutant hair follicles fail to undergo programmed regression, and instead continue to proliferate, producing follicular cysts and matricomas. These results provide definitive genetic evidence that epithelial Bmpr1a is required for completion of tooth morphogenesis, and regulates terminal differentiation and proliferation in postnatal hair follicles.

Pax3 functions at a nodal point in melanocyte stem cell differentiation

Most stem cells are not totipotent. Instead, they are partially committed but remain undifferentiated. Upon appropriate stimulation they are capable of regenerating mature cell types. Little is known about the genetic programmes that maintain the undifferentiated phenotype of lineage-restricted stem cells. Here we describe the molecular details of a nodal point in adult melanocyte stem cell differentiation in which Pax3 simultaneously functions to initiate a melanogenic cascade while acting downstream to prevent terminal differentiation. Pax3 activates expression of Mitf, a transcription factor critical for melanogenesis, while at the same time it competes with Mitf for occupancy of an enhancer required for expression of dopachrome tautomerase, an enzyme that functions in melanin synthesis. Pax3-expressing melanoblasts are thus committed but undifferentiated until Pax3-mediated repression is relieved by activated β-catenin. Thus, a stem cell transcription factor can both determine cell fate and simultaneously maintain an undifferentiated state, leaving a cell poised to differentiate in response to external stimuli.

Canonical WNT signaling promotes mammary placode development and is essential for initiation of mammary gland morphogenesis

Mammary glands, like other skin appendages such as hair follicles and teeth, develop from the surface epithelium and underlying mesenchyme; however, the molecular controls of embryonic mammary development are largely unknown. We find that activation of the canonical WNT/β-catenin signaling pathway in the embryonic mouse mammary region coincides with initiation of mammary morphogenesis, and that WNT pathway activity subsequently localizes to mammary placodes and buds. Several Wnt genes are broadly expressed in the surface epithelium at the time of mammary initiation, and expression of additional Wnt and WNT pathway genes localizes to the mammary lines and placodes as they develop. Embryos cultured in medium containing WNT3A or the WNT pathway activator lithium chloride (LiCl) display accelerated formation of expanded placodes, and LiCl induces the formation of ectopic placode-like structures that show elevated expression of the placode marker Wnt10b. Conversely, expression of the secreted WNT inhibitor Dickkopf 1 in transgenic embryo surface epithelium in vivo completely blocks mammary placode formation and prevents localized expression of all mammary placode markers tested. These data indicate that WNT signaling promotes placode development and is required for initiation of mammary gland morphogenesis. WNT signals play similar roles in hair follicle formation and thus may be broadly required for induction of skin appendage morphogenesis.

Diverse cutaneous side effects associated with BRAF inhibitor therapy: A clinicopathologic study

BACKGROUND Vemurafenib, a novel selective small molecule inhibitor of BRAF, has recently been shown to be effective in the treatment of melanomas harboring the BRAF V600E mutation. Similar to the broad-spectrum RAF inhibitor sorafenib, vemurafenib induces development of squamous cell carcinomas and keratoacanthomas as a side effect of therapy. OBJECTIVE We sought to detail additional cutaneous adverse effects of vemurafenib and a similar BRAF inhibitor, dabrafenib. METHODS We evaluated the clinical and histologic feature of skin side effects developing on vemurafenib or dabrafenib therapy in 14 patients. RESULTS Eight patients developed one or more squamous cell carcinomas, and 11 patients formed benign verrucous keratoses. Eight patients developed single lesions and/or widespread eruptions with histopathologic findings of acantholytic dyskeratosis, consistent with warty dyskeratomas and Darier- or Grover-like rashes, respectively. One patient developed palmoplantar hyperkeratosis, and darkening of existing nevi and new nevi within 2 months of starting vemurafenib. Side effects presented as early as 1 week after beginning therapy, with a mean time of onset of 12.6 weeks in our cohort. LIMITATIONS This study was limited by the small number of cases, all from a single institution. CONCLUSION Selective BRAF inhibitor therapy is associated with the development of malignant and benign growths, including keratoacanthoma-like squamous cell carcinomas, warty dyskeratomas, and verrucous keratoses, along with widespread eruptions with histologic features of acantholytic dyskeratosis. Given the potential for malignant lesions to develop on treatment, awareness of potential adverse effects of these agents is necessary, and a low threshold for biopsy of new growths is recommended.

Cutaneous Manifestations of DOCK8 Deficiency Syndrome

BACKGROUND Mutations in the dedicator of cytokinesis 8 gene (DOCK8) cause a combined primary immunodeficiency syndrome that is characterized by elevated serum IgE levels, depressed IgM levels, eosinophilia, sinopulmonary infections, cutaneous viral infections, and lymphopenia. Many patients with DOCK8 deficiency were previously thought to have a variant of Jobs syndrome. Distinguishing between DOCK8 deficiency and Jobs syndrome, also referred to as autosomal dominant hyper-IgE syndrome, on the basis of clinical findings alone is challenging. The discovery of the DOCK8 mutation has made it possible to differentiate the cutaneous manifestations of these hyper-IgE syndromes. OBSERVATIONS Twenty-one patients from 14 families with confirmed homozygous or compound heterozygous mutations in DOCK8 were evaluated. Clinical findings included dermatitis, asthma, food and environmental allergies, recurrent sinopulmonary infections, staphylococcal skin abscesses, and severe cutaneous viral infections. Malignant neoplasms, including aggressive cutaneous T-cell lymphoma, anal and vulvar squamous cell carcinomas, and diffuse large B-cell lymphoma, developed in 5 patients during adolescence and young adulthood. CONCLUSIONS DOCK8 deficiency and Jobs syndrome share several clinical features, including elevated serum IgE levels, dermatitis, recurrent sinopulmonary infections, and cutaneous staphylococcal abscesses. However, the presence of recalcitrant, widespread cutaneous viral infections, asthma, and food and environmental allergies, as well as the absence of newborn rash and coarse facies, favors the clinical diagnosis of DOCK8 deficiency. Rates of malignancy and overall mortality in patients with DOCK8 deficiency were higher than in those with Jobs syndrome, highlighting the value of distinguishing between these conditions and the importance of close monitoring for neoplasia.

Coxsackievirus A6-induced hand-foot-mouth disease.

IMPORTANCE Hand-foot-mouth disease (HFMD) is an acute, self-limited, highly contagious viral illness that commonly affects children younger than 5 years. It is most typically caused by enterovirus 71 or coxsackievirus A16 and results in asymptomatic infection or mild disease. Immunocompetent adults are rarely affected. Recently, there have been increasing reports of a more severe form of HFMD associated with fevers, joint pains, and widespread painful eruptions. Some of these patients required hospitalization for supportive care. These severe cases were most commonly caused by coxsackievirus A6. OBSERVATIONS We describe a 37-year-old white man with widespread, crusted, pruritic papules on the scalp, ears, and face and a purpuric and targetoid painful vesicular eruption on his hands and feet, with associated fevers, neurologic symptoms, and arthritis, who required hospitalization for supportive care. His infection with coxsackievirus A6 was confirmed based on polymerase chain reaction from his oral mucosa and cutaneous vesicle fluid. CONCLUSIONS AND RELEVANCE Dermatologists should be familiar with the severe variant of HFMD caused by coxsackievirus A6, include it in their differential diagnosis of acute febrile blistering diseases, and be aware that certain patients may require hospitalization.

Disseminated Microsporidiosis in an Immunosuppressed Patient

We report a case of disseminated microsporidiosis in a patient with multiple myeloma who had received an allogeneic stem cell transplant requiring substantial immunosuppression. The causative organism was identified as Tubulinosema acridophagus, confirming this genus of microsporidia as a novel human pathogen.

Cutaneous autoimmune effects in the setting of therapeutic immune checkpoint inhibition for metastatic melanoma

Therapeutic immune checkpoint blockade for metastatic melanoma has been associated with vitiligo, pruritus and morbilliform eruptions. Reports of other autoimmune skin disease in this setting are rare. We sought to expand the spectrum of cutaneous immune‐mediated effects related to immune checkpoint inhibitor therapy. In this report, we describe two unusual cutaneous reactions related to checkpoint inhibitor therapy, namely bullous pemphigoid (BP) and dermatitis herpetiformis. The development of BP and dermatitis herpetiformis in the context of checkpoint inhibitor therapy is consistent with previous investigations supporting the importance of effector and regulatory T cells in the pathogenesis of these diseases.

WNT10A mutation causes ectodermal dysplasia by impairing progenitor cell proliferation and KLF4-mediated differentiation

Human WNT10A mutations are associated with developmental tooth abnormalities and adolescent onset of a broad range of ectodermal defects. Here we show that β-catenin pathway activity and adult epithelial progenitor proliferation are reduced in the absence of WNT10A, and identify Wnt-active self-renewing stem cells in affected tissues including hair follicles, sebaceous glands, taste buds, nails and sweat ducts. Human and mouse WNT10A mutant palmoplantar and tongue epithelia also display specific differentiation defects that are mimicked by loss of the transcription factor KLF4. We find that β-catenin interacts directly with region-specific LEF/TCF factors, and with KLF4 in differentiating, but not proliferating, cells to promote expression of specialized keratins required for normal tissue structure and integrity. Our data identify WNT10A as a critical ligand controlling adult epithelial proliferation and region-specific differentiation, and suggest downstream β-catenin pathway activation as a potential approach to ameliorate regenerative defects in WNT10A patients.