B. Jack Longley

Diagnosis of gastrointestinal stromal tumors: a consensus approach.

As a result of major recent advances in understanding the biology of gastrointestinal stromal tumors (GIST), specifically recognition of the central role of activating KIT mutations and associated KIT protein expression in these lesions, and thedevelop-ment of novel and effective therapy for GISTs using thereceptor tyrosine kinase in hibitor STI-571, these tumors have become the focus of considerable attention among pathologists, clinicians, and patients. Stromal/mesenchymal tumors of the gastrointestinal tract have long been a sourceof confusion and controversy with regard to classification, line(s) of differentiation, and prognostication. Characterization of the KIT pathway and its phenotypic implications has helped to resolve some but not all of these issues. Given the now critical role of accurate and reproducible pathologic diagnosis in ensuring appropriate treatment for patients with GIST, the National Institutes of Health (NIH) convened a GIST workshop in April 2001 with the goal of developing a consensus approach to diagnosis and morphologic prognostication. Key elements of the consensus, as described herein, are the defining role of KIT immunopositivity indiagnosis and a proposed scheme for estimating metastatic riskin these lesions, based on tumor size and mitotic count, recognizing that it is probably unwise to use the definitive term benign for any GIST, at least at the present time.

SCF/c-kit signaling is required for cyclic regeneration of the hair pigmentation unit

ABSTRACT Hair graying, an age‐associated process of unknown etiology, is characterized by a reduced number and activity of hair follicle (HF) melanocytes. Stem cell factor (SCF) and its receptor c‐kit are impor¬tant for melanocyte survival during development, and mutations in these genes result in unpigmented hairs. Here we show that during cyclic HF regeneration in C57BL/6 mice, proliferating, differentiating, and mel¬anin‐producing melanocytes express c‐kit, whereas pre¬sumptive melanocyte precursors do not. SCF overex¬pression in HF epithelium significantly increases the number and proliferative activity of melanocytes. Dur¬ing the induced hair cycle in C57BL/6 mice, adminis¬tration of anti‐c‐kit antibody dose‐dependently de¬creases hair pigmentation and leads to partially depigmented (gray) or fully depigmented (white) hairs, associated with significant decreases in melanocyte proliferation and differentiation, as determined by immunostaining and confocal microscopy. However, in the next hair cycle, the previously treated animals grow fully pigmented hairs with the normal number and distribution of melanocytes. This suggests that melanocyte stem cells are not dependent on SCF/c‐kit and when appropriately stimulated can generate melanogenically active melanocytes. Therefore, the blockade of c‐kit signaling offers a fully reversible model for hair depigmentation, which might be used for the studies of hair pigmentation disorders.—Botchkareva, N. V., Khlgatian, M., Longley, B. J., Botchkarev, V. A., and Gilchrest, B. A. SCF/c‐kit signaling is required for cyclic regeneration of the hair pigmentation unit. FASEB J. 15, 645‐658 (2001)

Effects of tyrosine kinase inhibitor STI571 on human mast cells bearing wild-type or mutated c-kit

OBJECTIVE STI571 is a tyrosine kinase inhibitor which inhibits the kinase activity of kit, the receptor for stem cell factor (SCF). Because activating mutations of c-kit affecting codon 816 are associated with human mast cell neoplasms, we determined whether STI571 exerted a similar cytotoxic effect on neoplastic and normal human mast cells. METHODS We investigated the effect of addition of STI571 in increasing concentrations (0.01 to 10 micromolar) to two HMC-1 human mast cell leukemia cell lines carrying two different activating c-kit mutations in codons 816 or 560, as well as the effect of the drug on short-term bone marrow cultures obtained from patients who carry a mutated codon 816 or wild-type c-kit. RESULTS STI571 failed to inhibit the growth of HMC-1(560,816) cells bearing a codon 816 mutation but effectively suppressed the proliferation of HMC-1(560) carrying c-kit with the wild-type codon 816. STI571 did not induce preferential killing of neoplastic bone marrow mast cells in short-term cultures from patients bearing a codon 816 c-kit mutation. In contrast, STI571 caused a dramatic reduction in mast cells in patients without codon 816 c-kit mutations. CONCLUSION These results suggest that STI571, while effectively killing mast cells with wild-type c-kit, did not show preferential cytotoxicity to neoplastic human mast cells and thus may not be effective in the treatment of human systemic mastocytosis associated with codon 816 c-kit mutations.

Chemoprevention of skin cancer by grape constituent resveratrol: relevance to human disease?

According to the World Cancer Report, skin cancer constitutes ∼30% of all newly diagnosed cancers in the world, and solar ultraviolet (UV) radiation (particularly, its UVB component; 290–320 nm) is an established cause of ∼90% of skin cancers. The available options have proven to be inadequate for the management of skin cancers. Therefore, there is an urgent need to develop mechanism‐based novel approaches for prevention/therapy of skin cancer. In this study, we evaluated the chemopreventive effects of resveratrol against UVB radiation‐mediated skin tumorigenesis in the SKH‐1 hairless mouse model. For our studies, we used a UVB initiation‐promotion protocol in which the control mice were subjected to chronic UVB exposure (180 mJ/cm2, twice weekly, for 28 weeks). The experimental animals received either a pretreatment (30 min before each UVB) or post‐treatment (5 min after UVB) of resveratrol (25 or 50 micro mole/0.2 ml acetone/mouse). The mice were followed for skin tumorigenesis and were killed at 24 h after the last UVB exposure, for further studies. The topical application of skin with resveratrol (both pre‐ and post‐ treatment) resulted in a highly significant 1) inhibition in tumor incidence, and 2) delay in the onset of tumorigenesis. Interestingly, the post‐treatment of resveratrol was found to impart equal protection than the pretreatment; suggesting that resveratrol‐mediated responses may not be sunscreen effects. Because Survivin is a critical regulator of survival/death of cells, and its overexpression has been implicated in several cancers, we evaluated its involvement in chemoprevention of UVB‐mediated skin carcinogenesis by resveratrol. Our data demonstrated a significant 1) up‐regulation of Survivin (both at protein‐and mRNA‐ levels), 2) up‐regulation of phospho‐Survivin protein, and 3) down‐regulation of proapoptotic Smac/DIABLO protein in skin tumors; whereas treatment with resveratrol resulted in the attenuation of these responses. Our study also suggests that resveratrol enhanced apoptosis in UVB‐exposure‐mediated skin tumors. Our study, for the first time, demonstrated that 1) resveratrol imparts strong chemopreventive effects against UVB exposure‐mediated skin carcinogenesis (relevant to human skin cancers), and 2) the chemopreventive effects of resveratrol may, at least in part, be mediated via modulations in Survivin and other associated events. On the basis of our work, it is conceivable to design resveratrol‐containing emollient or patch, as well as sunscreen and skin‐care products for prevention of skin cancer and other conditions, which are believed to be caused by UV radiation.

INHIBITION OF SPONTANEOUS RECEPTOR PHOSPHORYLATION BY RESIDUES IN A PUTATIVE ALPHA -HELIX IN THE KIT INTRACELLULAR JUXTAMEMBRANE REGION

KIT receptor kinase activity is repressed, prior to stem cell factor binding, by unknown structural constraints. Using site-directed mutagenesis, we examined the role of KIT intracellular juxtamembrane residues Met-552 through Ile-563 in controlling receptor autophosphorylation. Alanine substitution for Tyr-553, Trp-557, Val-559, or Val-560, all sitting along the hydrophobic side of an amphipathic α-helix (Tyr-553–Ile-563) predicted by the Chou-Fasman algorithm, resulted in substantially increased spontaneous receptor phosphorylation, revealing inhibitory roles for these residues. Alanine substitution for other residues, most of which are on the hydrophilic side of the helix, caused no or slightly increased basal receptor phosphorylation. Converting Tyr-553 or Trp-557 to phenylalanine generated slight or no elevation, respectively, in basal KIT phosphorylation, indicating that the phenyl ring of Tyr-553 and the hydrophobicity of Trp-557 are critical for the inhibition. Although alanine substitution for Lys-558 had no effect on receptor phosphorylation, its substitution with proline produced high spontaneous receptor phosphorylation, suggesting that the predicted α-helical conformation is involved in the inhibition. A synthetic peptide comprising Tyr-553 through Ile-563 showed circular dichroism spectra characteristic of α-helix, supporting the structural prediction. Thus, the KIT intracellular juxtamembrane region contains important residues which, in a putative α-helical conformation, exert inhibitory control on the kinase activity of ligand-unoccupied receptor.

A Generalized Annular Eruption With Occasional Vesicles—Quiz Case

A 63-year-old woman presented with a 4-year history of a persistent, pruritic vesicular skin eruption. Her medical history was notable for psoriatic arthritis. There was no family history of autoimmune disease or immunobullous disorders. Examination revealed scattered annular and arcuate erythematous plaques with raised, slightly edematous borders studded with erosions and occasional vesicles. These lesions were located on her trunk, arms, and legs with relative sparing of her face and complete absence of mucous membrane involvement (Figure 1). Two biopsies were taken, one for routine hematoxylin-eosin staining (Figure 2) and the other for direct immunofluorescence (Figure 3). What is your diagnosis?

Serpiginous Erythematous Plaques on the Feet—Quiz Case

An 84-year-old man presented with a 1-month history of a progressively enlarging necrotic eschar on the dorsal surface of his left hand. He reported sustaining a superficial injury while fishing. The eschar did not respond to clindamycin and levofloxacin. His medical history was remarkable for non-Hodgkin lymphoma as well as interstitial pulmonary pneumonitis that was treated with prednisone and azathioprine. He was also taking trimethoprim-sulfamethoxazole for Pneumocystis jiroveci prophylaxis because of his concomitant immunosuppression and pulmonary infiltrates. Physical examination revealed a 3.5-cm black, necrotic eschar with surrounding induration on the dorsal surface of the left hand overlying the first web space (Figure 1). No axillary or epitrochlear lymphadenopathy was appreciated. An incisional biopsy specimen was obtained for histological analysis (Figure 2 and Figure 3). A complete blood cell count failed to reveal leukocytosis. What is your diagnosis?