The basal cell nevus syndrome (BCNS) is characterized by developmental abnormalities and by the postnatal occurrence of cancers, especially basal cell carcinomas (BCCs), the most common human cancer. Heritable mutations in BCNS patients and a somatic mutation in a sporadic BCC were identified in a human homolog of the Drosophila patched (ptc) gene. The ptc gene encodes a transmembrane protein that in Drosophila acts in opposition to the Hedgehog signaling protein, controlling cell fates, patterning, and growth in numerous tissues. The human PTC gene appears to be crucial for proper embryonic development and for tumor suppression.

https://science.sciencemag.org/content/sci/272/5268/1668.full.pdf

Human Homolog of patched, a Candidate Gene for the Basal Cell Nevus Syndrome

The search for genetic damage in neoplastic cells now occupies a central place in cancer research. Diverse examples of such damage are in hand, and they in turn hint at biochemical explanations for neoplastic growth. The way may be open to solve the riddles of how normal cells govern their replication and why cancer cells do not.

https://science.sciencemag.org/content/sci/235/4786/305.full.pdf

The molecular genetics of cancer

Chromosomal abnormalities in tumours were recognized at the end of the last century but their significance has only recently become clear. Distinct translocations in leukaemias and in solid tumours lead to the activation of proto-oncogene products or, more commonly, creation of tumour-specific fusion proteins. The proteins in both categories are often transcription factors and thus disruption of transcriptional control plays a major role in the aetiology of cancer. Fusion proteins formed after chromosomal translocations are common in a range of tumour types; these are unique tumour antigens and are therefore potential targets for therapy design.

Chromosomal translocations in human cancer.

Detection of minimal residual disease (MRD) has proven to provide independent prognostic information for treatment stratification in several types of leukemias such as childhood acute lymphoblastic leukemia (ALL), chronic myeloid leukemia (CML) and acute promyelocytc leukemia. This report focuses on the accurate quantitative measurement of fusion gene (FG) transcripts as can be applied in 35-45% of ALL and acute myeloid leukemia, and in more than 90% of CML. A total of 26 European university laboratories from 10 countries have collaborated to establish a standardized protocol for TaqMan-based real-time quantitative PCR (RQ-PCR) analysis of the main leukemia-associated FGs within the Europe Against Cancer EAC) program. Four phases were scheduled: (1) training, (2) optimization, (3) sensitivity testing and (4) patient sample testing. During our program, three quality control rounds on a large series of coded RNA samples were performed including a balanced randomized assay, which enabled final validation of the EAC primer and probe sets. The expression level of the nine major FG transcripts in a large series of stored diagnostic leukemia samples (n = 278) was evaluated. After normalization, no statistically significant difference in expression level was observed between bone marrow and peripheral blood on paired samples at diagnosis. However, RQ-PCR revealed marked differences in FG expression between transcripts in leukemic samples at diagnosis that could account for differential assay sensitivity. The development of standardized protocols for RQ-PCR analysis of FG transcripts provides a milestone for molecular determination of MRD levels. This is likely to prove invaluable to the management of patients entered into multicenter therapeutic trials.

http://www.rticc.org/2006-2012/docs/programas/documento-121381205176b457a69c8cff2223a24563374476707973e5f9.pdf

Standardization and quality control studies of ‘real-time’ quantitative reverse transcriptase polymerase chain reaction of fusion gene transcripts for residual disease detection in leukemia – A Europe Against Cancer Program

https://academiccommons.columbia.edu/doi/10.7916/D8NC6C9K/download

Chromosomal translocation t(15;17) in human acute promyelocytic leukemia fuses RARα with a novel putative transcription factor, PML

Chromosomal translocation t(1;19) results in synthesis of a homeobox fusion mRNA that codes for a potential chimeric transcription factor

Intraspecific human-human cell hybrids provide a stable model system with which to investigate the genetic control of transformed and tumorigenic phenotypes. Using this system it has been shown that these phenotypes are under separate genetic control. Furthermore, the tumorigenic phenotype can be complemented by fusion of different tumorigenic cells, resulting in nontumorigenic hybrids. This system also provides information on the control of differentiated function. Molecular cytogenetic techniques should reveal the nature of the chromosomal control of neoplastic transformation.

Human cell hybrids: analysis of transformation and tumorigenicity

The selective alteration of the cellular genome by laser microbeam irradiation has been extensively applied in cell biology. We report here the use of the third harmonic (355 nm) of an yttrium-aluminum garnet laser to facilitate the direct transfer of the neo gene into cultured human HT1080-6TG cells. The resultant transformants were selected in medium containing an aminoglycoside antibiotic, G418. Integration of the neo gene into individual human chromosomes and expression of the gene were demonstrated by Southern blot analyses, microcell-mediated chromosome transfer, and chromosome analyses. The stability of the integrated neo gene in the transformants was shown by a comparative growth assay in selective and nonselective media. Transformation and incorporation of the neo gene into the host genome occurred at a frequency of 8 X 10(-4)-3 X 10(-3). This method appears to be 100-fold more efficient than the standard calcium phosphate-mediated method of DNA transfer.

Direct gene transfer into human cultured cells facilitated by laser micropuncture of the cell membrane.

Human cell hybrids derived from malignant HeLa and normal fibroblast parental cells expressed many of the transformed properties of the HeLa parent but their tumor-producing capability was suppressed. Hybrids derived from HeLa/HeLa fusions retained both their transformed and malignant phenotypes. Thus, an apparent separation of the control of the transformed versus malignant phenotype is indicated. Furthermore, several transformed properties--including lack of density-dependent inhibition of growth, lectin agglutination, lowered requirement for serum growth factors, and anchorage independence--are expressed coordinately in the nontumorigenic hybrids. This finding suggests that none of these properties by themselves, or in concert, endows a cell with tumorigenic potential.

Analysis of malignancy in human cells: malignant and transformed phenotypes are under separate genetic control.

The association between anchorage independence and tumorigenicity was examined using a series of intraspecific human cell hybrids. The cell lines represented non-tumorigenic HeLa/fibroblast hybrids and tumorigenic segregants derived from them. These segregants had lost no more than 5% of the original chromosome complement. Both non-tumorigenic and tumorigenic cell populations formed colonies in methyl cellulose. The relative size of the colonies seemed to be inherited as a stable trait. Serial cloning of nontumorigenic hybrids in methyl cellulose led to an enhanced efficiency of colony formation but no selection for tumoregenic segregants. Thus, the property of anchorage independence is clearly dissociated from tumorigenicity in this human cell system. An ancillary observation was the chromosomal stability of the hybrids over many population doublings. This intraspecific human cell model therefore provides a genotypically and phenotypically stable system for examination of the genetic control of transformation and neoplasia.

Joyce Wilkinson

Papers

Chromosomal translocation t(1;19) results in synthesis of a homeobox fusion mRNA that codes for a potential chimeric transcription factor

Human cell hybrids: analysis of transformation and tumorigenicity

Direct gene transfer into human cultured cells facilitated by laser micropuncture of the cell membrane.

Analysis of malignancy in human cells: malignant and transformed phenotypes are under separate genetic control.

Dissociation of anchorage independence from tumorigenicity in human cell hybrids