Proliferation enhancement by spontaneous multiplication of chromosome 7 in rheumatic synovial cells in vitro

Safety of using cultured cells with trisomy 7 in cell therapy for treating osteoarthritis

Cell therapy is a promising alternative treatment approach currently under study for osteoarthritis (OA), the most common chronic musculoskeletal disease. However, the mesenchymal stem cells (MSCs) used in cell therapy to treat OA are usually expanded in vitro to obtain sufficient numbers for transplantation, and their safety has not been fully assessed from multiple perspectives. Analysis of karyotypic abnormalities, in particular, is important to ensure the safety of cells; however, chromosomal mutations may also occur during the cell-expansion process. In addition, there have been many reports showing chromosome abnormalities, mainly trisomy 7, in the cartilage and synovium of patients with OA as well as in normal tissues. The suitability of cells with these karyotypic abnormalities as cells for cell therapy has not been evaluated. Recently, we assessed the safety of using cells with trisomy 7 from the osteoarthritic joint of a patient for transplantation, and we followed up with the patient for 5 years. This study showed analysis for copy number variant and whole-genome sequencing, compared with blood DNA from the same patient. We did not find any abnormalities in the genes regardless of trisomy 7. No side effects were observed for at least 5 years in the human clinical study. This suggests that the transplantation of cultured cells with trisomy 7 isolated from an osteoarthritic joint and transplanted into the osteoarthritic joints of the same person is not expected to cause serious adverse events. However, it is unclear what problems may arise in the case of allogeneic transplantation. Different types of risks will also exist depending on other transplantation routes, such as localization to the knee-joint only or circulation inflow and lung entrapment. In addition, since the cause of trisomy 7 occurrence remains unclear, it is necessary to clarify the mechanism of trisomy 7 in OA to perform cell therapy for OA patients in a safe manner.

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Trisomy 7 is frequently observed in the cartilage and synovium of patients with OA.

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MSCs with trisomy 7 did not form tumor after transplantation into mice.

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No side effects were observed 5 years after transplantation of MSCs with trisomy 7.

Update on Tenosynovial Giant Cell Tumor, an Inflammatory Arthritis With Neoplastic Features

Rheumatoid arthritis (RA) is a chronic inflammatory disease that leads to joint destruction and bone erosion. Even if many treatments were developed with success in the last decades, some patients fail to respond, and disease chronicity is still a burden. Mechanisms involved in such resistance may include molecular changes in stromal cells. Other explanations can come from observations of tenosynovial giant cell tumor (TGCT), first considered as an inflammatory arthritis, but with unusual neoplastic features. TGCT leads to synovium hypertrophy and hyperplasia with hemosiderin deposition. It affects young adults, resulting in secondary osteoarthritis and increased morbidity. TGCT shows clinical, histological and genetic similarities with RA but affecting a single joint. However, the monoclonality of some synoviocytes, the presence of translocations and rare metastases also suggest a neoplastic disease, with some features common with sarcoma. TGCT is more probably in an intermediate situation between an inflammatory and a neoplastic process, with a main involvement of the proinflammatory cytokine CSF-1/CSF1R signaling axis. The key treatment option is surgery. New treatments, derived from the RA and sarcoma fields, are emerging. The tyrosine kinase inhibitor pexidartinib was recently FDA-approved as the first drug for severe TGCT where surgery is not an option. Options directly targeting the excessive proliferation of synoviocytes are at a preclinical stage.

Initial cell plating density affects properties of human primary synovial mesenchymal stem cells

Synovial mesenchymal stem cells (MSCs) appear to be an attractive cell source in cartilage and meniscus regeneration because of their high proliferative and chondrogenic potentials. Two methods are used to culture synovial nucleated cells in the preparation of primary synovial MSCs. In one method, the cells are plated at low density to make cell colonies. In the other method, the cells are plated at high density. We investigated the effects of initial cell density on proliferation, surface markers, and multipotentiality, including chondrogenesis in primary synovial MSCs. Human synovium was obtained from the knee joints of patients with osteoarthritis after total knee arthroplasty. Immediately after enzyme digestion, the synovial nucleated cells were plated in densities of 10³ , 10⁴ , or 10⁵  cells/60-cm² dish and cultured for 14 days. Proliferation, surface markers, chondrogenesis, adipogenesis, and calcification were examined in three populations. The cell colonies were distinct in the 10³  cells/dish group, faint in the 10⁴  cells/dish group, and obscure in the 10⁵  cells/dish group. The total number of cells/dish was positively related to plating density, whereas the fold increase was negatively related to plating density (n = 13). Among 12 surface markers, a negative relation to plating density was distinct in CD105. The cartilage pellet weight was negatively related to the initial plating density. The oil red-o positive area and alizarin red positive area were positively related to the initial plating density. The initial cell plating density affected the properties of primary synovial MSCs. Synovial nucleated cells proliferated better when plated at low density, and the synovial MSCs obtained by this method contained a high chondrogenic potential. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. J Orthop Res 37:1358-1367, 2019.

Synovium-Derived Mesenchymal Stem/Stromal Cells and their Promise for Cartilage Regeneration

Adult tissues are reservoirs of rare populations of cells known as mesenchymal stem/stromal cells (MSCs) that have tissue-regenerating features retained from embryonic development. As well as building up the musculoskeletal system in early life, MSCs also replenish and repair tissues in adult life, such as bone, cartilage, muscle, and adipose tissue. Cells that show regenerative features at least in vitro have been identified from several connective tissues. Bone marrow and adipose tissue are the most well recognized sources of MSCs that are already used widely in clinical practice. Regenerative medicine aims to exploit MSCs and their tissue regeneration even though the underlying mechanisms for their beneficial effects are largely unknown. Despite many studies that have used various tissue-derived MSCs, the most effective tissue source for orthopedic procedures still remains to be identified. Another question that needs to be addressed is how to evaluate autologous MSCs (i.e., patient derived). Previous studies have suggested the features of bone-marrow-derived MSCs can differ widely between individuals, and can be changed in particular in patients suffering from some forms of degenerative disorder, such as osteoarthritis. The synovium is a thin membrane that protects the synovial joints, and it is a rich source of MSCs that show great potential for regenerative medicine. Here, we review synovium-derived MSCs from reports on basic and clinical studies. We discuss their potential to treat cartilage defects caused by either degeneration or trauma, and what needs to be done in further research toward their better exploitation for joint regeneration.

Yields and chondrogenic potential of primary synovial mesenchymal stem cells are comparable between rheumatoid arthritis and osteoarthritis patients

BACKGROUND

Mesenchymal stem cells derived from the synovial membrane (synovial MSCs) are a candidate cell source for regenerative medicine of cartilage and menisci due to their high chondrogenic ability. Regenerative medicine can be expected for RA patients with the inflammation well-controlled as well as OA patients and transplantation of synovial MSCs would also be a possible therapeutic treatment. Some properties of synovial MSCs vary dependent on the diseases patients have, and whether or not the pathological condition of RA affects the chondrogenesis of synovial MSCs remains controversial. The purpose of this study was to compare the properties of primary synovial MSCs between RA and OA patients.

METHODS

Human synovial tissue was harvested during total knee arthroplasty from the knee joints of eight patients with RA and OA respectively. Synovial nucleated cells were cultured for 14 days. Total cell yields, surface markers, and differentiation potentials were analyzed for primary synovial MSCs.

RESULTS

Nucleated cell number per 1 mg synovium was 8.4 ± 3.9 thousand in RA and 8.0 ± 0.9 thousand in OA. Total cell number after 14-day culture/1 mg synovium was 0.7 ± 0.4 million in RA and 0.5 ± 0.3 million in OA, showing no significant difference between in RA and OA. Cells after 14-day culture were mostly positive for CD44, CD73, CD90, CD105, negative for CD45 both in RA and OA. There was no significant difference for the cartilage pellet weight and sGAG content per pellet between in RA and OA. Both oil red O-positive colony rate and alizarin red-positive colony rate were similar in RA and OA.

CONCLUSIONS

Yields, surface markers and chondrogenic potential of primary synovial MSCs in RA were comparable to those in OA. Synovium derived from RA patients can be the cell source of MSCs for cartilage and meniscus regeneration.

Arthroscopic Transplantation of Synovial Stem Cells Improves Clinical Outcomes in Knees With Cartilage Defects

BACKGROUND

Transplantation of mesenchymal stem cells (MSCs) is one possible strategy to achieve articular cartilage repair. We previously reported that synovial MSCs were highly proliferative and able to undergo chondrogenesis. We also found that placing a suspension of synovial MSCs on a cartilage defect for 10 minutes promoted cartilage repair in rabbit and pig models. However, the in vivo efficacy of this approach has not been tested clinically.

QUESTIONS/PURPOSES

We asked whether transplantation of synovial MSCs improves (1) MRI features, (2) histologic features, and (3) clinical evaluation scores in patients with cartilage defects in the knee?

METHODS

Patients with a symptomatic single cartilage lesion of the femoral condyle were indicated for inclusion in our study, and between April 2008 and April 2011, 10 patients were enrolled in this study. All patients completed followups of 3 years or more. The average followup period was 52 months (range, 37-80 months). Synovial MSCs were expanded with 10% autologous human serum for 14 days after digestion. For transplantation, the patient was positioned so that the cartilage defect was facing upward, and synovial MSC suspension was placed on the cartilage defect with a syringe under arthroscopic control. The defect with the applied suspension then was held in the upward position for 10 minutes. Five patients underwent concomitant ACL reconstructions, among whom two had meniscus suturing performed simultaneously. For MRI quantification, the cartilage defect was scored from 0 to 5. Second-look arthroscopy was performed for four patients and biopsy specimens were evaluated histologically. Clinical outcome was assessed using the Lysholm score and Tegner Activity Level Scale at final followup. Comparisons of MRI and Lysholm scores before and after treatment for each patient were analyzed using the Wilcoxon signed-rank test.

RESULTS

MRI score (median ± 95% CI) was 1.0 ± 0.3 before and 5.0 ± 0.7 after, and increased after treatment in each patient (p = 0.005). Second-look arthroscopy in four patients showed that the cartilage defect appeared to be qualitatively better in all cases. Histologic analyses showed hyaline cartilage in three patients and fibrous cartilage in one at the deep zone. The Lysholm score (median ± 95% CI) was 76 ± 7 before and 95 ± 3 after, and increased after treatment in each patient (p = 0.005). The Tegner Activity Level Scale did not decrease after treatment in each patient.

CONCLUSIONS

For this small initial case series, transplantation of synovial MSCs was effective in terms of MRI score, qualitative histology, and Lysholm score. The use of synovial MSCs has an advantage in that the cells can be prepared at passage 0 in only 14 days. Transplantation of synovial MSCs may be less invasive than mosaicplasty and autologous chondrocyte implantation. To conclusively show the effectiveness of this treatment requires comparative studies, especially with more established arthroscopic procedures, such as marrow stimulation techniques.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

A deletion in chromosome 6q is associated with human abdominal aortic aneurysm

Current efforts to identify the genetic contribution to abdominal aortic aneurysm (AAA) have mainly focused on the assessment of germ-line variants such as single-nucleotide polymorphisms. The aim of the present study was to assess the presence of acquired chromosomal aberrations in human AAA. Microarray data of ten biopsies obtained from the site of main AAA dilatation (AAA body) and three control biopsies obtained from the macroscopically non-dilated neck of the AAA (AAA neck) were initially compared with identified chromosomal aneuploidies using the Chromosomal Aberration Region Miner (ChARM) software. A commonly deleted segment of chromosome bands 6 (q22.1-23.2) was predicted within AAA biopsies. This finding was confirmed by quantitative real-time PCR (qPCR)-based DNA copy number assessments of an independent set of six AAA body and neck biopsies which identified a fold copy number change (∆KCt) of -1±0.35, suggesting the loss of one copy of the long interspersed nucleotide element type 1 (LINE-1) mapped to chromosome 6 (q22.1-23.2). The median relative genomic content of LINE-1 DNA was also reduced in AAA body compared with AAA neck biopsies (1.540 compared with 3.159; P=0.031). A gene important for vascular homoeostasis mapped to 6q23.1, connective tissue growth factor (CTGF), was assessed and found to be significantly down-regulated within AAA bodies compared with AAA necks (0.261 compared with 0.627; P=0.031), as determined by reverse transcription qPCR using total RNA as a template. Histology demonstrated marked staining for macrophages within AAA body biopsies. We found in vitro that the median relative genomic content of LINE-1 DNA in aortic vascular smooth muscle cells (AoSMCs) exposed to pro-inflammatory medium was ~1.5 times greater than that measured in control AoSMCs exposed to non-conditioned medium (3.044 compared with 2.040; P=0.015). Our findings suggest that acquired chromosomal aberrations associated with retrotransposon propagation may predispose to sporadic AAA.

The p53-PUMA axis suppresses iPSC generation

Mechanisms underlying the reprogramming process of induced pluripotent stem cells remain poorly defined. Like tumorigenesis, generation of induced pluripotent stem cells was shown to be suppressed by the Trp53 (p53) pathway, at least in part via p21Cdkn1a (p21)-mediated cell cycle arrest. Here we examine the role of PUMA, a pro-apoptotic mediator of p53, during somatic reprogramming in comparison to p21 in the p53 pathway. Using mouse strains deficient in these molecules, we demonstrate that PUMA is an independent mediator of the negative effect of p53 on induced pluripotent stem cell induction. PUMA deficiency leads to a better survival rate associated with reduced DNA damage and fewer chromosomal aberrations in induced pluripotent stem cells, whereas loss of p21 or p53 results in an opposite outcome. Given these new findings, PUMA may serve as a distinct and more desirable target in the p53 pathway for induced pluripotent stem cell generation, thereby having important implications for potential therapeutic applications of induced pluripotent stem cells.

Preparation of mononuclear cells from synovial tissue

In rheumatoid arthritis (RA), the synovium represents the predominant site of inflammation and joint destruction and is regarded as the key organ involved in disease pathogenesis. It has been studied in different ways over the last 30 yr, yielding information about the mechanisms involved in disease and remains the tool most proximal to understanding the pathogenesis of RA. This chapter outlines how both histological and in vitro studies of dissociated tissue played key roles in the development of biological anti-TNF-alpha therapy and provides detailed protocols used routinely in the laboratory to facilitate studies of RA synovium and its composite cell populations.

Somatic mosaicism of chromosome 7 in a highly proliferating melanocytic congenital naevus in a ring chromosome 7 patient

Ring chromosome 7 is a rare but well documented chromosomal aberration in man. So far at least 14 cases have been reported in the literature showing a variable but distinct pattern of phenotypic characteristics in affected individuals. Besides others, skin findings as pigmented naevi are especially frequent. Loss of chromosomal material from the terminal chromosome arms in the structurally abnormal ring chromosome 7 as well as somatic mosaicism with loss or gain of chromosome 7 has been suggested to be responsible for the clinical symptoms. We now report another case of a ring chromosome 7 in a 14-year-old boy with multiple remarkable congenital naevi, where we could demonstrate for the first time somatic mosaicism showing significant gain of chromosome 7 within a highly proliferating melanocytic congenital naevus (MCN).

Trisomy 7 in synovial fluid cells of patients with rheumatoid arthritis

OBJECTIVE

Recent studies revealed trisomy 7 as a chromosomal abnormality in non-neoplastic disorders such as rheumatoid arthritis (RA). In the present study, we investigated the presence of trisomy 7 in the synovial fluid cells of patients with RA using fluorescence in situ hybridisation (FISH) analysis.

METHODS

Synovial fluid from 15 patients with RA was collected from knee joints. The control group consisted of seven patients with traumatic synovial effusion in their knee joints. The arthrocenteses were performed under aseptic conditions. Dual-colour FISH analysis was performed using chromosome-7-specific LSI D7S522 (7q31) and chromosome-5-specific LSI EGR1 (5q31)/D5S721 (5p15.2) probes on the slides prepared from synovial fluid of RA patients and controls.

RESULTS

The slides of our cases were analysed using two different DNA probes. When the slides hybridised with chromosome-5-specific probes were analysed, no trisomic or monosomic cells were revealed in both patients and controls. However, in eight of 15 patients, trisomy 7 occurred in variable percentages of cells (23% to 48%) of synovial fluid. No monosomic 7 cells were detected in these specimens. All control cases were disomic for chromosome 7.

CONCLUSION

The results of the present investigation suggest that trisomy 7 may play a role in the pathogenesis of synovial hyperproliferation in RA.

Synovial fibroblasts and synovial macrophages from patients with rheumatoid arthritis and other inflammatory joint diseases show chromosomal aberrations

Chromosomal aberrations were investigated in nuclei extracted from synovial tissue and first-passage synovial fibroblasts (P-1 SFB, 98% enrichment) or macrophages (P-1 Mphi) from patients with rheumatoid arthritis (n=10). The findings were compared with those in other rheumatic diseases (osteoarthritis, n=14; reactive arthritis, n=1), as well as with those in chronic obstructive pulmonary disease (n=8). Controls were paired peripheral blood lymphocytes from arthritic patients, synovial tissue or SFB/Mphi from joint trauma/normals (n=9), and peripheral blood monocytes from normal donors (n=10). GTG banding of metaphase chromosomes and interphase fluorescence in situ hybridization with centromere-specific probes were used. Comparable chromosomal aberrations were observed in synovial tissue and P-1 SFB of patients with rheumatoid arthritis, osteoarthritis, and reactive arthritis (polysomy 7 and aneusomies of chromosomes 4, 8, 9, 12, and 18). Notably, aneusomies of chromosomes 4, 6, 7, 8, 9, 11, 12, and/or X were also detected in P-1 synovial Mphi from rheumatoid arthritis (90% of the cases), osteoarthritis (93%), and reactive arthritis (1/1), as well as bronchial Mphi from chronic obstructive pulmonary disease (25%). No aberrations were detected in paired peripheral blood lymphocytes (except for one osteoarthritis case with a karyotype 45,X[10]/46,XX[17]), or in peripheral blood monocytes and synovial tissue of normals/joint trauma. Because Mphi aberrations were common to chronic joint and pulmonary disease, chronic inflammatory stress may induce chromosomal aberrations with potential functional relevance in local mesenchymal cells and infiltrating leukocytes in an organ-independent fashion.

Proteoglycan production in disomic and trisomy 7-carrying human synovial cells

To gain further insight into the synthesis and structure of the synovial matrix of joints, we have established cell cultures from synovial specimens and elaborated their production of hyaluronan and proteoglycans. The cultures secreted mainly the small proteoglycan decorin, but also considerable amounts of the related biglycan and the large proteoglycan versican. Only minor amounts of heparan sulfate proteoglycans were found. All cultures also had a high production of hyaluronan, which highlights the important role for normal joint function of these cells. In joint diseases, a common feature is the presence of an extra chromosome 7 (trisomy 7) in the synovial cells. To study the possible consequences of trisomy 7 on the synovial cell function, we extended our study to cultures that had been sub-cloned to contain high amounts of trisomy 7-carrying cells. These cell cultures had approximately four times more versican than their disomic counterparts in the cell culture medium, indicating that versican may be a mediator in the processes of joint destructive disorders. To find an explanation for this increase in versican, we investigated the expression/secretion of PDGF-AA and IL-6, cytokines with their genes located to chromosome 7. Indeed, both these cytokines were increased in the cultures with high frequencies of trisomy 7. We then added the two cytokines to cell cultures of disomic synovial cells, but only cells treated with IL-6 displayed an increased amount of versican. Thus, we suggest that the increased amount of versican in cultures of trisomy 7-carrying cells relates to an autocrine loop involving an increased IL-6 production.

Analysis of the distribution and frequency of trisomy 7 in vivo in synovia from patients with osteoarthritis and pigmented villonodular synovitis

Osteoarthritis (OA) and pigmented villonodular synovitis (PVNS) are disorders associated with trisomy 7. The aim of the present study was to determine the frequency and distribution of the cells with +7 in vivo by analyzing sections of paraffin-embedded synovia from patients affected by OA, PVNS, other forms of synovitis [hemorragic synovitis (HS) and chronic synovitis (CS)], and from individuals without joint disease. Fluorescence in situ hybridization (FISH), using a centromeric probe for chromosome 7, showed that the mean frequency of trisomic nuclei in 5-microm sections was highest in PVNS (9.0%), followed by CS (5.9%), OA (5.6%), and HS (4.6%), whereas trisomic nuclei were rare (0.7%) in normal tissue. When 8-microm sections were studied, the frequencies of trisomic cells in OA and control synovia increased to 6.7% and 1.5%, respectively. Trisomic nuclei were found in all cases, including those for which cytogenetic analysis of short-term cultures had not disclosed any trisomic cells. Overall, the trisomic cells were scattered within the tissue. However, small clusters of cells with +7 were found in three cases. By hematoxylin-eosin staining of the slides used for FISH analysis it could be shown that the clustered trisomic cells were proliferating synoviocytes within villous extensions of the synovial membrane.

Isolation and characterization of rheumatoid arthritis synovial fibroblasts from primary culture--primary culture cells markedly differ from fourth-passage cells

To reduce culture artifacts by conventional repeated passaging and long-term culture in vitro, the isolation of synovial fibroblasts (SFB) was attempted from rheumatoid arthritis (RA) synovial membranes by trypsin/collagenase digest, short-term in vitro adherence (7 days), and negative isolation using magnetobead-coupled anti-CD14 monoclonal antibodies. This method yielded highly enriched SFB (85% prolyl-4-hydroxylase+/74% Thy-1/CD90+ cells; <2% contaminating macrophages; <1% leukocytes/endothelial cells) that, in comparison with conventional fourth-passage RA-SFB, showed a markedly different phenotype and significantly lower proliferation rates upon stimulation with platelet-derived growth factor and IL-1beta. This isolation method is simple and reliable, and may yield cells with features closer to the in vivo configuration of RA-SFB by avoiding extended in vitro culture.

Mosaic chromosomal aberrations in synovial fibroblasts of patients with rheumatoid arthritis, osteoarthritis, and other inflammatory joint diseases

Chromosomal aberrations were comparatively assessed in nuclei extracted from synovial tissue, primary-culture (P-0) synovial cells, and early-passage synovial fibroblasts (SFB; 98% enrichment; P-1, P-4 [passage 1, passage 4]) from patients with rheumatoid arthritis (RA; n = 21), osteoarthritis (OA; n = 24), and other rheumatic diseases. Peripheral blood lymphocytes (PBL) and skin fibroblasts (FB) (P-1, P-4) from the same patients, as well as SFB from normal joints and patients with joint trauma (JT) (n = 4), were used as controls. Analyses proceeded by standard GTG-banding and interphase centromere fluorescence in situ hybridization. Structural chromosomal aberrations were observed in SFB (P-1 or P-4) from 4 of 21 RA patients (19%), with involvement of chromosome 1 [e.g. del(1)(q12)] in 3 of 4 cases. In 10 of the 21 RA cases (48%), polysomy 7 was observed in P-1 SFB. In addition, aneusomies of chromosomes 4, 6, 8, 9, 12, 18, and Y were present. The percentage of polysomies was increased in P-4. Similar chromosomal aberrations were detected in SFB of OA and spondylarthropathy patients. No aberrations were detected in i) PBL or skin FB from the same patients (except for one OA patient with a karyotype 45,X[10]/46,XX[17] in PBL and variable polysomies in long-term culture skin FB); or ii) synovial tissue and/or P-1 SFB of normal joints or of patients with joint trauma. In conclusion, qualitatively comparable chromosomal aberrations were observed in synovial tissue and early-passage SFB of patients with RA, OA, and other inflammatory joint diseases. Thus, although of possible functional relevance for the pathologic role of SFB in RA, these alterations probably reflect a common response to chronic inflammatory stress in rheumatic diseases.

Novel mutations of the MET proto-oncogene in papillary renal carcinomas

Hereditary papillary renal carcinoma (HPRC) is characterized by multiple, bilateral papillary renal carcinomas. Previously, we demonstrated missense mutations in the tyrosine kinase domain of the MET proto-oncogene in HPRC and a subset of sporadic papillary renal carcinomas. In this study, we screened a large panel of sporadic papillary renal carcinomas and various solid tumors for mutations in the MET proto-oncogene. Summarizing these and previous results, mutations of the MET proto-oncogene were detected in 17/129 sporadic papillary renal carcinomas but not in other solid tumors. We detected five novel missense mutations; three of five mutations were located in the ATP-binding region of the tyrosine kinase domain of MET. One novel mutation in MET, V1110I, was located at a codon homologous to an activating mutation in the c-erbB proto-oncogene. These mutations caused constitutive phosphorylation of MET when transfected into NIH3T3 cells. Molecular modeling studies suggest that these activating mutations interfere with the intrasteric mechanism of tyrosine kinase autoinhibition and facilitate transition to the active form of the MET kinase. The low frequency of MET mutations in noninherited papillary renal carcinomas (PRC) suggests that noninherited PRC may develop by a different mechanism than hereditary papillary renal carcinoma.

Inherited carcinomas of the kidney

Studies of families with inherited carcinomas have provided powerful tools to identify the genes involved in the pathogenesis of human cancers. In this review, we summarize the clinical, pathological, and genetic characteristics of the inherited carcinomas of the kidney. We emphasize the observation that different genes predispose to histologically different types of renal carcinoma. Hereditary papillary renal carcinoma, a recently described inherited disorder, is discussed in detail along with the predisposing gene, the MET protooncogene. The data support a classification of renal carcinomas based on molecular genetics.