The structural basis of differential DNA sequence recognition by restriction-modification controller proteins.

Controller (C) proteins regulate the expression of restriction-modification (RM) genes in a wide variety of RM systems. However, the RM system Esp1396I is of particular interest as the C protein regulates both the restriction endonuclease (R) gene and the methyltransferase (M) gene. The mechanism of this finely tuned genetic switch depends on differential binding affinities for the promoters controlling the R and M genes, which in turn depends on differential DNA sequence recognition and the ability to recognize dual symmetries. We report here the crystal structure of the C protein bound to the M promoter, and compare the binding affinities for each operator sequence by surface plasmon resonance. Comparison of the structure of the transcriptional repression complex at the M promoter with that of the transcriptional activation complex at the R promoter shows how subtle changes in protein-DNA interactions, underpinned by small conformational changes in the protein, can explain the molecular basis of differential regulation of gene expression.

Recognition of dual symmetry by the controller protein C.Esp1396I based on the structure of the transcriptional activation complex.

The controller protein C.Esp1396I regulates the timing of gene expression of the restriction-modification (RM) genes of the RM system Esp1396I. The molecular recognition of promoter sequences by such transcriptional regulators is poorly understood, in part because the DNA sequence motifs do not conform to a well-defined symmetry. We report here the crystal structure of the controller protein bound to a DNA operator site. The structure reveals how two different symmetries within the operator are simultaneously recognized by the homo-dimeric protein, underpinned by a conformational change in one of the protein subunits. The recognition of two different DNA symmetries through movement of a flexible loop in one of the protein subunits may represent a general mechanism for the recognition of pseudo-symmetric DNA sequences.

Cutaneous changes in fibrous hamartoma of infancy.

BACKGROUND: Fibrous hamartoma of infancy (FHI) is a fast growing soft tissue tumor that usually arises in the first 2 years of life. The histology of the lesion has been well described. Few studies, however, have looked at changes in the overlying skin and its appendages. METHODS: A database search performed at British Columbia Children's Hospital yielded 15 cases of unequivocal FHI occurring in 12 patients (three were recurrences). Of these, we were able to retrieve 13. Five of 13 cases had sections including epidermis. These slides were reviewed with specific emphasis on skin adnexae. RESULTS: Of the cases with excised epidermis in continuity with the lesion, 5/5 had eccrine changes, including hyperplasia, duct dilatation, intraluminal papillary formations, and squamous syringometaplasia. One case showed epidermal basaloid follicular hyperplasia. CONCLUSIONS: This study shows that eccrine changes are frequently seen in cases of FHI when overlying skin is sampled. This may be a useful clue to consider this diagnosis, especially when the biopsy is superficial.

Kaposiform hemangioendothelioma: a locally aggressive vascular tumor.

Kaposiform hemangioendothelioma is a locally aggressive, endothelial-derived spindle cell neoplasm that occurs exclusively in infants and adolescents. Lesions are characterized by rapid growth and extension, and are often associated with Kasabach-Merritt syndrome and lymphangiomatosis. Clinically nonspecific, they can appear as tender rapidly expanding red plaques, nodules, grouped papules, or telangiectasias. The histology is distinctive, however, as it combines features of tufted angioma, progressive lymphangioma, and Kaposi's sarcoma in a characteristic pattern. We describe a patient with kaposiform hemangioendothelioma currently controlled with systemic prednisone.

Possible origin of pancreatic fat necrosis as a septal panniculitis.

We describe pancreatic subcutaneous fat necrosis in a man with alcoholism and pancreatitis. The initial specimen, from a 2-day-old lesion, showed a septal inflammatory infiltrate in the subcutis. A second specimen, from a 5-day-old lesion, showed the lobular pattern of enzymatic fat necrosis diagnostic for pancreatic panniculitis. We suggest that the histologic appearance of subcutaneous pancreatic fat necrosis evolves from an early septal reaction to a fully developed lobular panniculitis.

Melanocytic nevi with focal atypical epithelioid cell components: a review of seventy-three cases.

BACKGROUND: We report a variant of melanocytic nevus that may be confused with melanoma. OBJECTIVE: The purpose of this study is to describe the clinical, histologic, and biologic features of nevi with focal atypical epithelioid cell components (clonal nevi). METHODS: Seventy-three cases were retrieved by reviewing lesions previously diagnosed as clonal, combined, deep penetrating, and inverted type-A nevi. Histologic features were assessed and referring physicians received a questionnaire about the presentation and outcome of each case. RESULTS: Histologically, all cases had a biphasic pattern characterized by an ordinary nevus that contained a darkly pigmented collection of large distinct epithelioid melanocytes in the superficial dermis. Immunostains identified mutant p53 proteins in 50% of dermal clones (9 of 18) but not in ordinary nevus cells adjacent to the clones. We are not aware of any patient developing a malignant melanoma (mean follow-up 24.5 months), including 41 cases that were initially incompletely excised. CONCLUSION: Clonal nevi are a distinct variant of melanocytic nevi and should be distinguished from malignant melanoma arising in a preexisting nevus.

Ras mutations in human melanoma: a marker of malignant progression.

In this study we address whether there is an association between ras mutations and disease progression in malignant melanoma. DNA was extracted from 100 paraffin-embedded melanomas and sequences around the 12th, 13th and 61st codons of N-, H-, and K-ras were amplified using the polymerase chain reaction and probed for single base pair mutations using synthetic oligonucleotide probes. Thirty-six melanomas contained mutations, which in 25 cases (69%) occurred at the 61st codon of N-ras. The results from dot blot hybridizations were confirmed by subcloning and sequencing the polymerase chain reaction products from two tumors. No ras mutations were found in Clark's level I melanomas, whereas 19% of level II and 45% of the more advanced primary tumors contained ras mutations (Chi squared test: p < 0.05). The median Breslow thickness of primary melanomas with ras mutations was 0.72 mm, significantly thicker than the 0.42 mm of melanomas without mutations (Mann-Whitney U test, p = 0.042). Ras mutations were found more frequently in primary tumors from continuously exposed skin (56%) than tumors from intermittently or non-sun exposed sites (21%). Fifty percent of locally recurrent and 47% of metastatic melanomas had ras mutations. We conclude that ras mutations occur in a subset of melanomas from sun-exposed skin as a feature of tumor progression.

Crystalglobulinemia syndrome. A manifestation of multiple myeloma.

BACKGROUND: Crystalglobulinemia syndrome (CS) is a rare vasculopathy that may arise as a complication of multiple myeloma (MM). METHODS AND RESULTS: A patient with multiple myeloma in whom crystalglobulinemia syndrome was the initial manifestation with polyarthralgias, cutaneous ulceration, and lower limb ischemia requiring bilateral amputations is reported. CONCLUSION: The rare syndrome of crystalglobulinemia may be associated with multiple myeloma, so it is important that clinicians be aware of this syndrome and its clinical and morphologic features.

Hepatolithiasis in hereditary hemorrhagic telangiectasia.

Hereditary hemorrhagic telangiectasia is a rare, hereditary fibrovascular dysplasia. We report a case associated with hepatolithiasis. Hepatolithiasis, relatively common in East Asia, is rare in the West. The association of the two conditions has not been previously reported. In this case, vascular malformations in the liver gave rise to arteriovenous and arterioportal fistulas, causing arteriovenous shunting and protal hypertension, respectively. Abnormal blood flow is the proposed mechanism for the hepatic fibrosis and nodular regeneration. Hepatic fibrosis, by causing stenosis of large intrahepatic bile ducts, bile stasis, and secondary infection, is the hypothesized mechanism for calculus formation. Hepatolithiasis ultimately caused death from acute bacterial cholangitis and septicemia.

Pleural multicystic mesothelial proliferation. The so-called multicystic mesothelioma.

We report on the clinical and pathological features of a hitherto unrecognized multicystic and multifocal mesothelial lesion arising in the pleural cavity of a 37-year-old Caucasian woman. The lesions consisted of clusters of thin-walled cysts separated by connective tissue and lined by a single layer of flattened and cuboidal mesothelium. Mucin stains, immunohistochemistry, and electron microscopy were consistent with a mesothelial origin. The pathological features are identical to those of the previously reported multicystic mesotheliomas of the peritoneum. Although these multicystic peritoneal mesothelial lesions have been regarded as neoplasms, absent stromal extension, lack of mitotic activity, and (in this case) continuity with morphologically normal surrounding mesothelium are suggestive of a reactive process. The term "multicystic mesothelial proliferation" may therefore be more appropriate. Because these lesions may be detected as discrete pleural based masses on chest radiograph and CT scan, they may be submitted for frozen section during operative resection. It is therefore important to be aware of their existence, morphology, and differential diagnosis.

Intestinal differentiation in ovarian mucinous tumours.

Fifty-five ovarian mucinous tumours, 22 benign, 16 borderline and 17 malignant, were examined for intestinal differentiation (ID). This was defined by the presence of one or more of endocrine, absorptive, goblet or Paneth cells, and identified by routine haematoxylin and eosin as well as histochemical and immunoperoxidase techniques. Twenty benign (91%), 14 borderline (88%) and all malignant tumours contained foci of ID. The frequency of ID was not significantly different between the mucinous tumour types (chi-squared test for independence). Follow-up was available on all patients with borderline tumours: 14 were stage Ia, including both cases without ID, and 2 were stage Ic at presentation. All are alive and free of disease at 9-39 months (median 15.5 months). We conclude that the presence of ID in borderline mucinous tumours is unlikely to be of prognostic significance, and that a subdivision of these tumours into müllerian and intestinal types is unnecessary.