Carlos Monteagudo

Engineered control of cell morphology in vivo reveals distinct roles for yeast and filamentous forms of Candida albicans during infection

ABSTRACT It is widely assumed that the ability of Candida albicans to switch between different morphologies is required for pathogenesis. However, most virulence studies have used mutants that are permanently locked into either the yeast or filamentous forms which are avirulent but unsuitable for discerning the role of morphogenetic conversions at the various stages of the infectious process. We have constructed a strain in which this developmental transition can be externally modulated both in vitro and in vivo. This was achieved by placing one copy of the NRG1 gene (a negative regulator of filamentation) under the control of a tetracycline-regulatable promoter. This modified strain was then tested in an animal model of hematogenously disseminated candidiasis. Mice injected with this strain under conditions permitting hyphal development succumbed to the infection, whereas all of the animals injected under conditions that inhibited this transition survived. Importantly, fungal burdens were almost identical in both sets of animals, indicating that, whereas filament formation appears to be required for the mortality resulting from a deep-seated infection, yeast cells play an important role early in the infectious process by extravasating and disseminating to the target organs. Moreover, these infecting Candida yeast cells still retained their pathogenic potential, as demonstrated by allowing this developmental transition to occur at various time points postinfection. We demonstrate here the importance of morphogenetic conversions in C. albicans pathogenesis. This engineered strain should provide a useful tool in unraveling the individual contributions of the yeast and filamentous forms at various stages of the infectious process.

Clinicopathological and immunohistochemical analysis of 20 cases of Merkel cell carcinoma in search of prognostic markers.

Aims:  To evaluate the clinicopathological and immunohistochemical characteristics of Merkel cell carcinoma (MCC) in an attempt to find new, potentially significant, prognostic markers.

Expression levels of a filament-specific transcriptional regulator are sufficient to determine Candida albicans morphology and virulence

Candida albicans, the major human fungal pathogen, undergoes a reversible morphological transition from single yeast cells to pseudohyphal and hyphal filaments (elongated cells attached end-to-end). Because typical C. albicans infections contain a mixture of these morphologies it has, for many years, been difficult to assess the relative contribution of each form to virulence. In addition, the regulatory mechanisms that determine growth in pseudohyphal and hyphal morphologies are largely unknown. To address these questions we have generated a C. albicans strain that can be genetically manipulated to grow completely in the hyphal form under non-filament-inducing conditions in vitro. This was achieved by inducing high-level constitutive expression of UME6, a recently identified filament-specific transcriptional regulator of C. albicans hyphal extension. We show that high-level UME6 expression significantly increases hyphal formation and promotes virulence in a mouse model of systemic candidiasis. Our results strongly suggest that shifting the morphology of a C. albicans population toward the hyphal form, and/or increasing hyphal-specific gene expression, during the course of infection is sufficient to improve virulence potential. We also demonstrate that lower levels of UME6 expression specify growth largely in the pseudohyphal form and that increasing UME6 levels is sufficient to cause cells to gradually shift from pseudohyphal to hyphal morphology. In addition, we show that UME6 levels differentially induce the expression of several known filament-specific transcripts. These findings suggest that a common transcriptional regulatory mechanism functions to specify both pseudohyphal and hyphal morphologies in a dosage-dependent manner.

UME6, a Novel Filament-specific Regulator of Candida albicans Hyphal Extension and Virulence

The specific ability of the major human fungal pathogen Candida albicans, as well as many other pathogenic fungi, to extend initial short filaments (germ tubes) into elongated hyphal filaments is important for a variety of virulence-related processes. However, the molecular mechanisms that control hyphal extension have remained poorly understood for many years. We report the identification of a novel C. albicans transcriptional regulator, UME6, which is induced in response to multiple host environmental cues and is specifically important for hyphal extension. Although capable of forming germ tubes, the ume6Delta/ume6Delta mutant exhibits a clear defect in hyphal extension both in vitro and during infection in vivo and is attenuated for virulence in a mouse model of systemic candidiasis. We also show that UME6 is an important downstream component of both the RFG1-TUP1 and NRG1-TUP1 filamentous growth regulatory pathways, and we provide evidence to suggest that Nrg1 and Ume6 function together by a negative feedback loop to control the level and duration of filament-specific gene expression in response to inducing conditions. Our results suggest that hyphal extension is controlled by a specific transcriptional regulatory mechanism and is correlated with the maintenance of high-level expression of genes in the C. albicans filamentous growth program.

Dermatofibrosarcoma protuberans: a comprehensive review and update on diagnosis and management

Dermatofibrosarcoma protuberans (DFSP) is a rare superficial tumor characterized by high rates of local recurrence and low risk of metastasis. DFSP occurs most commonly on the trunk and proximal extremities, affects all races, and often develops between the second and fifth decade of life. The tumor grows slowly, typically over years. Histologically, several variants of DFSP have been described and should be well characterized to avoid misdiagnosis with other tumors. These include pigmented (Bednar tumor), myxoid, myoid, granular cell, sclerotic, atrophic DFSP, giant cell fibroblastoma, and DFSP with fibrosarcomatous areas. Of all these variants, only the DFSP with fibrosarcomatous areas is high grade, with a higher rate of local recurrence and distant metastasis. DFSP is genetically characterized by the t(17;22)(q22;q13), resulting in the fusion of alpha chain type 1 of collagen gene and platelet-derived growth factor beta gene. This translocation is present in 90% of DFSP and represents a very useful tool in the differential diagnosis of DFSP with other tumors with similar histology. The standard treatment is wide local excision with at least a 2-cm margin. However, local recurrence after apparently adequate surgical excision is well recognized. Mohs micrographic surgery would be the treatment of choice with a better cure rate and maximal conservation of tissue. When surgery is insufficient, clinical evidence has suggested that imatinib mesylate is a safe and effective treatment in DFSP, especially in cases of local advanced or metastatic disease. This article presents an overview of the state of the art in the clinicopathological management of this disease.

Inhibition of Filamentation Can Be Used To Treat Disseminated Candidiasis

ABSTRACT Candida albicans remains the leading causative agent of invasive fungal infection. Although the importance of filamentation in C. albicans pathogenesis has been extensively investigated, in vivo studies to date have been unable to dissect the role of this developmental process in the establishment of infection versus the development of active disease as characterized by damage to the host leading to mortality. To address this issue, we genetically engineered a C. albicans tet-NRG1 strain in which filamentation and virulence can be modulated both in vitro and in vivo simply by the presence or absence of doxycycline (DOX): this strain enabled us, in a prior study, to demonstrate that yeast-form cells were able to infect the deep organs but caused no disease unless filamentation (induced by the addition of DOX) was allowed to occur. In the present study, we examined whether inhibiting filamentation (by withdrawing the DOX) at 24 or 48 h postinfection could serve as an effective therapeutic intervention against candidiasis. The results obtained indicate that DOX removal led to an alteration in the morphology of the infecting fungal cells and a dramatic increase in survival, but as with conventional antifungal drug therapy regimens, mortality rates increased markedly the longer this intervention was delayed. These observations reinforce the importance of invasive filamentous growth in causing the damage to the host and the lethality associated with active disease and suggest this process could be fruitfully targeted for the development of new antifungal agents.

CXCR3 chemokine receptor immunoreactivity in primary cutaneous malignant melanoma : correlation with clinicopathological prognostic factors

Background: A role for CXCR3, the receptor for chemokines Mig, IP-10 and interferon-inducible T cell α-chemoattractant, in tumour cell migration during melanoma progression has been proposed. Aims: To analyse CXCR3 expression in primary cutaneous malignant melanomas and its comparison with clinicopathological and prognostic factors. Methods: A retrospective immunohistochemical study was carried out on formalin-fixed paraffin-wax-embedded sections from 82 patients with primary invasive cutaneous melanomas, with a monoclonal antibody to CXCR3 (clone 49801.111; R&D Systems). Immunoreactivity was semiquantitatively evaluated: labelling intensity (0, absent; 1, weak; 2, moderate; 3, strong) multiplied by the percentage of cells in each of the four intensity categories. A positive staining was considered when the score was >100. Melanomas were categorised by age, sex, primary site, tumour thickness, growth phase, ulceration, lymphocytic infiltration, recurrence, lymph node and distant metastasis, and survival. Univariate and multivariate statistical analyses were carried out. Results: Of the 82 patients, a positive CXCR3 staining was found in 26 (31.7%) patients, whereas 56 (68.3%) were negative. In univariate analysis, a significant association of CXCR3-positive tumour cell immunostaining with tumour thickness >1 mm (p = 0.003), absence of lymphocytic infiltration (p = 0.04) and the presence of distant metastasis (p = 0.048) was found. Multivariate analysis found tumour thickness as the only independent factor with considerable association with distant metastases. Conclusions: Our findings of a positive correlation of CXCR3 tumour cell immunoreactivity in human primary cutaneous melanoma with tumour thickness >1 mm and absence of intratumoral lymphocytic infiltration support the biological implication of CXCR3 in the tumour progression of cutaneous malignant melanoma.

Dermatofibrosarcoma protuberans: clinical, pathological, and genetic (COL1A1‐PDGFB ) study with therapeutic implications

Aims: To analyse the presence of collagen type I alpha 1–platelet‐derived growth factor beta (COL1A1–PDGFB) transcripts in 20 cases of dermatofibrosarcoma protuberans (DFSP) and to assess the relationship between COL1A1 breakpoints and clinical and histopathological variables.

Diagnostic value of CD34 immunostaining in desmoplastic trichilemmoma

Desmoplastic trichilemmoma (DT) is a variant of trichilemmoma, characterized by a central prominent desmoplastic component which may simulate invasive carcinoma. We have studied the morphologic and immunohistochemical features of seven cases of DT. Immunohistochemistry was performed on paraffin sections using monoclonal antibodies to CD34 (QBEND/10), vimentin and GCDFP‐15. CD34 was also tested in seven cases of basal cell carcinoma (BCC), three with outer root sheath differentiation and four with morphea‐form features, and five squamous cell carcinomas. Histologically, features of conventional trichilemmoma were seen at the periphery of the seven lesions. In contrast, at the center, the epithelial cells tended to cluster in narrow irregular cords and nests entrapped in a dense collagenous stroma. One case of DT coexisted with a BCC. In all cases of DT, epithelial tumor cells showed CD34 immunostaining. All cases of BCC, including the one contiguous to a DT, were CD34 negative. CD34 immunodetection in the epithelial cells of the pseudoinvasive component of DT may be of great value in the differential diagnosis with other desmoplastic tumors of the skin, and particularly with BCC.

Molecular diagnosis of dermatofibrosarcoma protuberans: a comparison between reverse transcriptase-polymerase chain reaction and fluorescence in situ hybridization methodologies.

Dermatofibrosarcoma protuberans (DFSP) is characterized by the presence of the t(17;22)(q22;q13) that leads to the fusion of the COL1A1 and PDGFB genes. This translocation can be detected by multiplex reverse transcriptase‐polymerase chain reaction (RT‐PCR) or fluorescence in situ hybridization (FISH) techniques. We have evaluated the usefulness of a dual color dual fusion FISH probe strategy for COL1A1/PDGFB detection in a series of 103 archival DFSPs and compared the obtained results with RT‐PCR analyses. FISH and RT‐PCR were carried out on paraffin embedded tissue samples. Regarding the RT‐PCR approach, all COL1A1 exons and exon 2 of PDGFB were evaluated. Sensitivity, specificity, positive and negative predictive values were assessed considering the histological diagnosis as the gold standard. We also analyzed the relationship between the genetic findings and the clinicopathological variables of the tumors. The COL1A1/PDGFB translocation was detected in 93% of DFSP. Both techniques showed a similar specificity (100%), but FISH was more sensitive than RT‐PCR (90% vs. 72%). Regarding, clinicopathological features, a higher percentage of positive cells detected by FISH was significantly associated with the fibrosarcomatous DFSP variant (P < 0.001). Interestingly, all CD34 negative DFSP (n = 5) were positive for COL1A1/PDGFB translocation by both techniques. In conclusion, the majority of DFSP harbor the COL1A1/PDGFB translocation and FISH technique should be recommended as a routine diagnostic tool, especially in cases showing unusual histopathological subtypes and/or immunohistochemical features.