c-Ha-ras-1 alleles in bladder cancer, Wilms' tumour and malignant melanoma

A "molecular evolution" approach for isolation of intrinsically active (MEK-independent) MAP kinases

Mitogen-activated protein (MAP) kinases are a large family of enzymes composed of about four subfamilies, each containing several isoforms and splicing variants. Many MAP kinases are coexpressed in each eukaryotic cell and coactivated in response to various stimuli. It is, therefore, difficult to explore the specific downstream effects of each species of MAPK. Expression of an intrinsically active variant of a MAPK, while other MAPKs are not active, allows for tracking of a specific array of substrates, target genes, and biological/pathological effects corresponding to the expressed molecule. This chapter describes a method for obtaining such intrinsically active MAPKs. Because of the unique mode of MAPK activation, which is absolutely dependent on unconventional phosphorylation (on neighboring Thr + Tyr residues), a rational design of mutations that would render the kinase intrinsically active is currently unfeasible. Our method is based, therefore, on a "Molecular Evolution" approach that uses the power of yeast genetics and is unbiased toward the mutation sites. We describe in detail how to prepare a large population of randomly mutated molecules of the desired MAPK and how to screen this library in a yeast strain lacking the relevant MAPK kinase (MAPKK). The idea is to identify MAPK variants that are fulfilling all MAPK functions and allow growth of this strain - namely, MAPK molecules that function biologically in the complete absence of their upstream activator. We further describe the details of the "plasmid-loss" assay used for distinguishing between true positive and false positive clones. Finally, we report on a new yeast strain lacking four MAPKKs that could serve as a universal target for screening for active MAPK of all subfamilies.

MAP-quest: could we produce constitutively active variants of MAP kinases?

Constitutively active mutants that acquired intrinsic activity and escaped regulation, serve as powerful tools for revealing the biochemical, biological and pathological functions of proteins. Such mutants are not available for mitogen-activated protein kinases (MAPKs). It is not known how to mimic the unusual mode of MAPK activation and to enforce, by mutations, their active conformation. In this review we describe the strategies employed in attempts to overcome this obstacle. We focus on a recent breakthrough with the p38 family that suggests that active variants of all MAPKs will soon be available.

HRAS1 variable number of tandem repeats polymorphism and risk of bladder cancer

The HRAS1 variable number of tandem repeats (VNTR) polymorphism, 1 kb downstream from the HRAS1 gene, has been reported to be associated with risk of various cancers. To examine whether individuals with rare HRAS1 VNTR alleles are at increased risk of bladder cancer we carried out a case control study with 230 bladder cancer cases and 203 hospital-based controls frequency-matched on ethnicity, gender and age. For genotyping we used a PCR-based long-gel electrophoretic assay that provides precise allele size discrimination. We did not find evidence of a strong overall effect of the HRAS1 VNTR on bladder cancer risk. Genotype data for whites and blacks were analyzed separately, but the number of black subjects was too small to estimate meaningful odds ratios. Compared to white subjects with 2 common alleles, the odds ratio (OR) for white subjects with 1 rare allele was 0.9 (95% confidence interval (CI) = 0.5-1.4) and for those with 2 rare alleles OR = 1.7 (95% CI = 0.6-5.4). HRAS1 genotype may be related to the prognosis of bladder cancer, however, because incident cases, i.e., newly diagnosed cases had a higher frequency of rare alleles than did prevalent cases, i.e., cases already existing at the time of recruitment. Repeating the analyses with incident cases only (n = 53), the OR for subjects with 1 rare allele was 1.2 (95% CI = 0.6-2.4) and for those with 2 rare alleles 3.2 (95% CI = 0.8-13.7). The number of incident cases was too small to draw firm conclusions on a possible association with a subgroup of tumors with a poor prognosis. Published 2002 Wiley-Liss, Inc.

Studies of the c-Harvey-Ras gene in psychiatric disorders

Hérault et al. (1993) previously reported a significant association between autism and the larger fragments of the c-Harvey-Ras (HRAS) Bam H1 polymorphism. We have sought to verify this finding and determine if there was any evidence for an association with other psychiatric disorders. Because of its greater sensitivity, we have examined the HRAS Msp 1 polymorphism. We found a just significant increase in the prevalence of the > 2.1 kb alleles in 48 subjects with autism versus 50 control subjects. There was no increase in the prevalence of the > 2.1 kb alleles in 164 probands with Tourette's syndrome. Examination of 16 preselected symptom clusters, however, showed a significant trend toward higher scores for obsessive-compulsive and phobic symptoms in > 2.1 kb homozygotes. While this locus requires further study, in conjunction with the results of Hérault et al., the present findings suggest that genetic defects in HRAS, and possibly other components of the G protein secondary messenger system, may play a role in some psychiatric disorders.

An association between the risk of cancer and mutations in the HRAS1 minisatellite locus

BACKGROUND

The role of mutations in protooncogenes and their regulatory sequences in the pathogenesis of cancer is under close scrutiny. Minisatellites are unstable repetitive sequences of DNA that are present throughout the human genome. The highly polymorphic HRAS1 minisatellite locus just downstream from the protooncogene H-ras-1 consists of four common progenitor alleles and several dozen rare alleles, which apparently derive from mutations of the progenitors. We previously observed an association of the rare mutant alleles with many forms of cancer, and we undertook the present study to pursue this observation further.

METHODS

We conducted a case-control study, typing 736 HRAS1 alleles from patients with cancer and 652 from controls by Southern blotting of leukocyte DNA. We also carried out a meta-analysis of this study and 22 other published studies, estimating the relative risk of cancer (such as bladder, breast, or colorectal cancer) when one of the rare HRAS1 alleles was present.

RESULTS

Both the present case-control study (odds ratio, 1.83; 95 percent confidence interval, 1.28 to 2.67; P = 0.002) and the present study combined with our previous study (odds ratio, 2.07; 95 percent confidence interval, 1.47 to 2.92; P < 0.001), as well as the meta-analysis of all 23 studies (odds ratio, 1.93; 95 percent confidence interval, 1.63 to 2.30; chi-square = 57.58; P < 0.001), replicated our original finding and demonstrated a significant association of rare HRAS1 alleles with cancer. We found significant associations for four types of cancer: carcinomas of the breast, colorectum, and urinary bladder and acute leukemia. We also identified suggestive but not statistically significant associations for cancers of the lung and prostate and for non-Hodgkin's lymphoma.

CONCLUSIONS

Mutant alleles of the HRAS1 minisatellite locus represent a major risk factor for common types of cancer. Although the relative risk associated with the presence of one rare allele is moderate, the aggregate prevalence of one rare allele is moderate, the aggregate prevalence of this class of mutant alleles implies an extremely important attributable risk: 1 in 11 cancers of the breast, colorectum, and bladder.

Rare HRAS1 alleles outside the VTR region in lymph nodes from patients with malignant lymphoma

We found a new type of rare HRAS1 alleles arising de novo in the lymph node of lymphoma patients. Rare alleles of 6.2 kb (a0.1) and 7.3 kb (a2.3) are displayed in the presence of common alleles of 6.6 kb (a1) and 7.6 kb (a3), respectively. These rare alleles lack nucleotide sequences, present in the common alleles in the 5' part between the BamHI and XmaIII site. In addition, the rare alleles may have the classic A-G mutation in the intron at position 2719. In contrast to what is observed for rare constitutional alleles, the VTR region of these rare alleles has the same size as the common alleles. At present the significance of this new type of alleles is not clear.

Molecular genetics of human malignant melanoma

Due to a variety of known and unknown control mechanisms, the human genome is remarkably stable when compared to most other species. The long latency periods of most solid tumors, during which the cell undergoes malignant transformation, are presumably due to this stability. The molecular basis responsible for the induction of genetic instability and the resultant biological characteristics manifest in tumor populations is not well understood. The discovery of both oncogenes and tumor suppressor genes, however, has placed the phenomenon of human genome stability on a more solid conceptual footing. These types of genes clearly place multiple barriers to oncogenic transformation, and traversing these barriers apparently requires both time and the accumulation of genetic defects that cannot be corrected. The evolution of neoplasias can, therefore, be predicted to be due to: (1) consistent and progressive loss of tumor suppressor genes; (2) gene amplification, resulting in the over-expression of proteins that aid in tumor progression; (3) gene mutation, which alters the orderly biochemistry of the normal cell; (4) genes that allow a cell like the melanocyte to escape the confining nature of the epidermis and to invade through the dermis into the circulatory and lymphatic systems in order to disseminate itself to other organs (e.g., proteolytic enzymes, enzyme inhibitors, integrins, metastases genes, chemotactic factors etc.); (5) factors, perhaps such as TGF beta 2, that may impact negatively on MHC antigens and confuse host defense mechanisms; and (6) S.O.S.-type genes, which may be expressed as a direct response to the accumulating damage in an attempt to correct the damage, but that may then become part of the problem instead of the solution. The extraordinary plasticity and instability of the genome of a melanoma cell suggests an inordinate amount of genetic flux. In addition to activating and inactivating various genes, this constant shuffling and rearranging of the genome in neoplasms such as MM may be constantly altering gene dose. Cytogenetic and molecular biological studies have been the Rosetta stone for understanding the etiological relevant genetic events in human cancers. Genetic alterations fundamental to the pathology of MM have begun to be defined. Studies designed to understand these perturbations at the biochemical and organismic level are underway.(ABSTRACT TRUNCATED AT 400 WORDS)

Ha-ras polymorphisms in epithelial ovarian cancer

Unusual restriction fragment length polymorphisms (RFLPs) of the Ha-ras locus have been found in DNA from leukocytes and tumor tissue of cancer patients. To determine whether rare alleles would be observed frequently in patients with ovarian cancer, Ha-ras RFLPs were studied in DNA from 42 different ovarian epithelial tumors and from the peripheral blood leukocytes of 76 normal individuals. Four common, seven intermediate, and seven rare alleles were detected overall. Similar fractions of rare alleles were found in DNA from ovarian cancers and from the peripheral blood of normal individuals. Thus, the frequency of unusual Ha-ras RFLPs did not distinguish patients with ovarian cancers from apparently healthy individuals.

Association between restriction fragment length polymorphism of the L-myc gene and lung metastasis in human breast cancer

EcoRI restriction fragment length polymorphism (RFLP) of the L-myc gene was examined in leukocyte DNAs isolated from 381 breast cancer patients. No differences in the patterns of L-myc RFLP were found between breast cancer patients and healthy individuals. However, among 97 patients who relapsed, a statistical correlation was found between L-myc RFLP and lung metastases (p less than 0.05). These results are in close agreement with previous findings in patients with cancer of the lung, bone or kidney, and suggest that L-myc RFLP may be a useful marker for predicting lung metastasis in some human cancers.

Distribution of Ha-ras alleles in patients with colorectal cancer and Crohn's disease

The allele distribution of the Ha-ras gene on chromosome 11p was analysed by the restriction fragment length polymorphism of the enzymes Mspl/Hpall in 238 individuals. The investigation covered 116 patients with colorectal carcinoma and 122 patients with Crohn's disease, representing two patient populations with the same ethnic origin, one with a malignant and the other a benign disease of the same organ system. A total of 17 different alleles were detected belonging to the common, intermediate, and rare classes according to the original nomenclature of Ha-ras alleles. Patients with Crohn's disease showed no difference in the distribution of Ha-ras alleles when compared with expected frequencies. In patients with colorectal carcinoma, the frequency of rare alleles was significantly increased compared with the patients with Crohn's disease (chi 2 = 8.166; Fisher's exact test = 0.005) and with a reference population of 424 cancer free individuals (chi 2 = 49.312; Fisher's exact test = 0.000). Homozygosity was not detected for any rare allele. The occurrence of a rare Ha-ras allele was not linked to the location of the colorectal tumour. These results confirm the hypothesis that unique Ha-ras alleles represent an inherited factor which predisposes the development of colorectal cancer.

Lack of evidence of Ki-ras codon 12 mutations in melanocytic lesions

A number of studies have failed to detect point mutations at codon 12 in the Ki-ras gene in melanocytic neoplasms. One recent study, however, has found a high percentage of Ki-ras codon 12 point mutations. In an effort to resolve this difference, the present study examined noncultured melanocytic lesions (i.e., 5 benign nevi, 10 dysplastic nevi, and 8 primary melanomas: 4 in situ and 4 invasive) for point mutations at codon 12 in the first exon of the Ki-ras proto-oncogene using polymerase chain reaction methodology with oligonucleotide hybridization and direct DNA sequencing. The results of this study indicates no detectable mutations in the 12th codon of the first exon of the Ki-ras gene in any premalignant or malignant melanocytic lesion examined.

Molecular mechanisms of ultraviolet radiation carcinogenesis

UV radiation is a potent DNA damaging agent and a known inducer of skin cancer in experimental animals. There is excellent scientific evidence to indicate that most non-melanoma human skin cancers are induced by repeated exposure to sunlight. UV radiation is unique in that it induces DNA damage that differs from the lesions induced by any other carcinogen. The prevalence of skin cancer on sun-exposed body sites in individuals with the inherited disorder XP suggests that defective repair of UV-induced DNA damage can lead to cancer induction. Carcinogenesis in the skin, as elsewhere, is a multistep process in which a series of genetic and epigenetic events leads to the emergence of a clone of cells that have escaped normal growth control mechanisms. The principal candidates that are involved in these events are oncogenes and tumor suppressor genes. Oncogenes display a positive effect on transformation, whereas tumor suppressor genes have an essentially negative effect, blocking transformation. Activated ras oncogenes have been identified in human skin cancers. In most cases, the mutations in the ras oncogenes have been localized to pyrimidine-rich sequences, which indicates that these sites are probably the targets for UV-induced DNA damage and subsequent mutation and transformation. The finding that activation of ras oncogenes in benign and self-regressing keratoacanthomas in both humans and in animals indicates that they play a role in the early stages of carcinogenesis (Corominas et al., 1989; Kumar et al., 1990). Since cancers do not arise immediately after exposure to physical or chemical carcinogens, ras oncogenes must remain latent for long periods of time. Tumor growth and progression into the more malignant stages may require additional events involving activation of other oncogenes or deletion of growth suppressor genes. In addition, amplification of proto-oncogenes or other genes may also be involved in tumor induction or progression. In contrast to the few studies that implicate the involvement of oncogenes in UV carcinogenesis, the role of tumor suppressor genes in UV carcinogenesis is unknown. Since cancer-prone individuals, particularly XP patients, lack one or more repair pathways, one can speculate that DNA repair enzymes would confer susceptibility to both spontaneous and environmentally induced cancers. Another potential candidate that can function as a tumor suppressor gene is the normal c-Ha-ras gene. Spandidos and Wilkie (1988) have shown that the normal c-Ha-ras gene can suppress transformation induced by the mutated ras gene.(ABSTRACT TRUNCATED AT 400 WORDS)

Ha-ras-1 alleles in Norwegian lung cancer patients

We have examined DNA restriction fragment length polymorphisms (RFLP) of the Ha-ras-1 gene in DNA from 118 lung cancer patients and 123 unaffected controls. When DNA samples were digested with MspI/HpaII restriction endonucleases. Southern blot analysis demonstrated 4 common, 4 intermediate and 7 different rare alleles in the combined population after hybridization to the pGDa1 probe. Six of the rare alleles were unique for the lung cancer group and 1 rare allele for the control group. The frequency of rare alleles in lung cancer patients (10/236) was significantly different (P less than 0.01) from the control group (1/246). The lung cancer group also had a significantly lower frequency of the common 2.57 kb fragment than the controls (P less than 0.02). The results thus indicate that Ha-ras genotyping may be of value in lung cancer risk assessment.

Detection of somatic mutations in tumours of diverse types by DNA fingerprinting with M13 phage DNA

Hybridization of M13 phage DNA to Southern blots of human DNA produces an individual-specific DNA fingerprint. In this study, tumour and lymphocyte DNA from a series of patients with melanoma, Merkel-cell carcinoma, Burkitt's lymphoma and Wilms' tumour was probed with M13 DNA to detect somatic mutations in the DNA of the tumours. Somatic changes were observed in tumour DNA of 16 out of the 28 cases examined. This frequency compared favourably with the frequency with which tumour-specific changes have been found when using the Jeffreys DNA fingerprinting probe 33.15, and demonstrates that M13 DNA provides a useful additional probe for the study of somatic changes in tumours. The finding that multiple DNA fragments were lost or gained in DNA fingerprints from individual tumours indicates a marked degree of complexity in the genetic changes involved in the evolution of certain human cancers.

Elevated frequency of a specific allele of the L-myc gene in male patients with bone and soft-tissue sarcomas

Restriction fragment length polymorphisms (RFLPs) of 2 oncogenes, c-Ha-ras and L-myc, have been analyzed in 101 patients with bone and soft-tissue sarcoma and in 98 normal individuals. The c-Ha-ras gene was highly polymorphic both in sarcoma patients and in normal individuals. In contrast to our previous observation in breast cancer patients (Honda et al., 1988), no significant difference in allele frequencies between normal and sarcoma populations was observed. The L-myc locus revealed 2-allele polymorphism, allele L (10-kb) and S (6.6-kb), after digestion with Eco RI. The allele frequencies of L and S in sarcoma patients were 0.381 and 0.619, respectively, and those in normal individuals were 0.485 and 0.515, respectively. While the distributions of alleles in both populations fitted well with the Hardy-Weinberg equilibrium, the frequency of the S allele was significantly higher in sarcoma patients than in normal individuals (p less than 0.05). When sarcoma patients were divided into male and female subpopulations, this difference was highly significant only in males (p less than 0.01) but not in females. Our results suggest that males carrying the S allele may be prone to develop sarcoma.

Restriction fragment length polymorphisms of L-myc and myb in human leukaemia and lymphoma in relation to age-selected controls

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Origin of rare Ha-ras alleles: relationship of VTR length to a 5' polymorphic Xho I site

Amongst the four common Ha-ras alleles in both controls and cancer patients, we detected the presence of a polymorphic Xho I site associated specifically with the 6.6 and 7.7 kb Bam HI fragments but absent from the 7.1 and 8.2 kb alleles, as recently reported by others. We have extended this study and report here, the consistent appearance of this Xho I site in unusual alleles close in size to the two common alleles of 6.6 and 7.7 kb, in control lymphoblastoid DNA samples in a variety of tumor DNAs. Unusual alleles grouped around the 7.1 and 8.2 kb common alleles on the other hand, did not possess the Xho I site. The consistent presence of the Xho I site polymorphism, in the unusual Ha-ras alleles surrounding the 6.6 and 7.7 kb common alleles and its absence in alleles around the 7.1 and 8.2 kb common alleles, suggests that the unusual ones are derived from the corresponding common alleles to which they are closest in size.

The EcoRI RFLP of c-mos in patients with non-Hodgkin's lymphoma and acute lymphoblastic leukemia, compared to geriatric and non-geriatric controls

We have used Southern blot analysis to type individuals for the presence or absence of a rare EcoRI RFLP at the c-mos proto-oncogene locus. This polymorphism has previously been reported to be associated with cancer. Ninety-eight patients with non-Hodgkin's lymphoma (NHL) or acute lymphoblastic leukemia (ALL) and 154 cancer-free individuals, including 108 geriatric patients with no family history of cancer, were studied. Because 4 geriatric patients (aged 67-94) were found to have the rate c-mos allele (A2), and the frequency of this A2 allele was no higher among the lymphoma/leukemia patients than among cancer-free individuals, it is unlikely that it constitutes a marker for NHL or ALL.

Partial deletion of chromosome 11p in breast cancer correlates with size of primary tumour and oestrogen receptor level

In a study of DNAs from 100 breast cancer patients and 100 controls, there were no differences in the frequencies of common or rare alleles at the Harvey ras (c-Ha-ras) locus on chromosome 11. However, one Ha-ras allele was deleted from the tumour DNA in 14 of 65 informative patients. Loss of a Ha-ras allele correlates with paucity of oestrogen receptor protein and with increased tumour size at presentation, but is not associated with microscopic evidence of lymph node invasion. The findings on Ha-ras and other informative loci are consistent with the possibility that a tumour suppressor gene involved in the early stages of breast cancer is located on the short arm of chromosome 11.

A Taqi RFLP of the human TGF alpha gene is significantly associated with cutaneous malignant melanoma

A TaqI restriction fragment length polymorphism (RFLP) of the human transforming growth factor alpha (hTGF alpha) locus was analyzed in DNA from 63 normal individuals, 34 malignant melanoma (MM) cell lines, and 18 melanoma biopsy specimens. The frequency of a 2.7-kb allele (0.18) in MM cell lines was significantly higher (p less than 0.01) than in lymphoblastoid cell lines (LCLs) derived from unaffected controls (0.05). The frequency (0.14) in MM biopsies was similar to that in MM cell lines although, owing to the small numbers investigated, it was not significantly higher than in controls. In the case of 5 MM patients who were constitutionally heterozygous for alleles at the TGF alpha locus, no apparent losses of heterozygosity were observed in the corresponding tumour DNA. Thus, the constitutional presence of the 2.7-kb allele may be a risk factor for melanoma.