From aneuploidy to cancer: the evolution of a new species?

Transmissible Cancer Evolution: The Under-Estimated Role of Environmental Factors in the “Perfect Storm” Theory

Although the true prevalence of transmissible cancers is not known, these atypical malignancies are likely rare in the wild. The reasons behind this rarity are only partially understood, but the “Perfect Storm hypothesis” suggests that transmissible cancers are infrequent because a precise confluence of tumor and host traits is required for their emergence. This explanation is plausible as transmissible cancers, like all emerging pathogens, will need specific biotic and abiotic conditions to be able to not only emerge, but to spread to detectable levels. Because those conditions would be rarely met, transmissible cancers would rarely spread, and thus most of the time disappear, even though they would regularly appear. Thus, further research is needed to identify the most important factors that can facilitate or block the emergence of transmissible cancers and influence their evolution. Such investigations are particularly relevant given that human activities are increasingly encroaching into wild areas, altering ecosystems and their processes, which can influence the conditions needed for the emergence and spread of transmissible cell lines.

Somatic Sex: On the Origin of Neoplasms With Chromosome Counts in Uneven Ploidy Ranges

Stable aneuploid genomes with nonrandom numerical changes in uneven ploidy ranges define distinct subsets of hematologic malignancies and solid tumors. The idea put forward herein suggests that they emerge from interactions between diploid mitotic and G0/G1 cells, which can in a single step produce all combinations of mono-, di-, tri-, tetra- and pentasomic paternal/maternal homologue configurations that define such genomes. A nanotube-mediated influx of interphase cell cytoplasm into mitotic cells would thus be responsible for the critical nondisjunction and segregation errors by physically impeding the proper formation of the cell division machinery, whereas only a complete cell fusion can simultaneously generate pentasomies, uniparental trisomies as well as biclonal hypo- and hyperdiploid cell populations. The term "somatic sex" was devised to accentuate the similarities between germ cell and somatic cell fusions. A somatic cell fusion, in particular, recapitulates many processes that are also instrumental in the formation of an abnormal zygote that involves a diploid oocyte and a haploid sperm, which then may further develop into a digynic triploid embryo. Despite their somehow deceptive differences and consequences, the resemblance of these two routes may go far beyond of what has hitherto been appreciated. Based on the arguments put forward herein, I propose that embryonic malignancies of mesenchymal origin with these particular types of aneuploidies can thus be viewed as the kind of flawed somatic equivalent of a digynic triploid embryo.

Spontaneous Cancers, But Not Many Induced Ones in Animals, Resemble Semi-New Organisms that Possess a Unique Programmed Cell Death Mode Different from Apoptosis, Senescent Death, Necrosis and Stress-Induced Cell Death

There are four basic cell death modes in animals, i.e. physiological senescent death (SD) and apoptosis as well as pathological necrosis and stress-induced cell death (SICD). There have been numerous publications describing “apoptosis” in cancer, mostly focused on killing cancer cells using radio- or chemo-therapy, with few on exploring how cancer cells die naturally without such treatments. Spontaneous benign or malignant neoplasms are immortal and autonomous, but they still retain some allegiance to their parental tissue or organ and thus are still somewhat controlled by the patient's body. Because of these properties of immortality, semi-autonomy, and semi-allegiance to the patient's body, spontaneous tumors have no redundant cells and resemble “semi-new organisms” parasitizing the patients, becoming a unique tissue type possessing a hitherto unannotated cell death mode besides SD, apoptosis, necrosis and SICD. Particularly, apoptosis aims to expunge redundant cells, whereas this new mode does not. In contrast to spontaneous tumors, many histologically malignant tumors induced in experimental animals, before they reach an advanced stage, regress after withdrawal of the inducer. This mortal and non-autonomous nature disqualifies these animal lesions as authentic neoplasms and as semi-new organisms but makes them a good tissue type for apoptosis studies. Ruminating over cell death in spontaneous cancers and many inauthentic tumors induced in animals from these new slants makes us realize that “whether cancer cells undergo apoptosis” is not an easy question with a simple answer. Our answer is that cancer cells have an uncharacterized programmed cell death mode, which is not apoptosis.

Evaluating the Remote Control of Programmed Cell Death, with or without a Compensatory Cell Proliferation

Organisms and their different component levels, whether organelle, cellular or other, come by birth and go by death, and the deaths are often balanced by new births. Evolution on the one hand has built demise program(s) in cells of organisms but on the other hand has established external controls on the program(s). For instance, evolution has established death program(s) in animal cells so that the cells can, when it is needed, commit apoptosis or senescent death (SD) in physiological situations and stress-induced cell death (SICD) in pathological situations. However, these programmed cell deaths are not predominantly regulated by the cells that do the dying but, instead, are controlled externally and remotely by the cells' superior(s), i.e. their host tissue or organ or even the animal's body. Currently, it is still unclear whether a cell has only one death program or has several programs respectively controlling SD, apoptosis and SICD. In animals, apoptosis exterminates, in a physiological manner, healthy but no-longer needed cells to avoid cell redundancy, whereas suicidal SD and SICD, like homicidal necrosis, terminate ill but useful cells, which may be followed by regeneration of the live cells and by scar formation to heal the damaged organ or tissue. Therefore, “who dies” clearly differentiates apoptosis from SD, SICD and necrosis. In animals, apoptosis can occur only in those cell types that retain a lifelong ability of proliferation and never occurs in those cell types that can no longer replicate in adulthood. In cancer cells, SICD is strengthened, apoptosis is dramatically weakened while SD has been lost. Most published studies professed to be about apoptosis are actually about SICD, which has four basic and well-articulated pathways involving caspases or involving pathological alterations in the mitochondria, endoplasmic reticula, or lysosomes.

Learning about the Importance of Mutation Prevention from Curable Cancers and Benign Tumors

Some cancers can be cured by chemotherapy or radiotherapy, presumably because they are derived from those cell types that not only can die easily but also have already been equipped with mobility and adaptability, which would later allow the cancers to metastasize without the acquisition of additional mutations. From a viewpoint of biological dispersal, invasive and metastatic cells may, among other possibilities, have been initial losers in the competition for resources with other cancer cells in the same primary tumor and thus have had to look for new habitats in order to survive. If this is really the case, manipulation of their ecosystems, such as by slightly ameliorating their hardship, may prevent metastasis. Since new mutations may occur, especially during and after therapy, to drive progression of cancer cells to metastasis and therapy-resistance, preventing new mutations from occurring should be a key principle for the development of new anticancer drugs. Such new drugs should be able to kill cancer cells very quickly without leaving the surviving cells enough time to develop new mutations and select resistant or metastatic clones. This principle questions the traditional use and the future development of genotoxic drugs for cancer therapy.

Just like the rest of evolution in Mother Nature, the evolution of cancers may be driven by natural selection, and not by haphazard mutations

Sporadic carcinogenesis starts from immortalization of a differentiated somatic cell or an organ-specific stem cell. The immortalized cell incepts a new or quasinew organism that lives like a parasite in the patient and usually proceeds to progressive simplification, constantly engendering intermediate organisms that are simpler than normal cells. Like organismal evolution in Mother Nature, this cellular simplification is a process of Darwinian selection of those mutations with growth- or survival-advantages, from numerous ones that occur randomly and stochastically. Therefore, functional gain of growth- or survival-sustaining oncogenes and functional loss of differentiation-sustaining tumor suppressor genes, which are hallmarks of cancer cells and contribute to phenotypes of greater malignancy, are not drivers of carcinogenesis but are results from natural selection of advantageous mutations. Besides this mutation-load dependent survival mechanism that is evolutionarily low and of an asexual nature, cancer cells may also use cell fusion for survival, which is an evolutionarily-higher mechanism and is of a sexual nature. Assigning oncogenes or tumor suppressor genes or their mutants as drivers to induce cancer in animals may somewhat coerce them to create man-made oncogenic pathways that may not really be a course of sporadic cancer formations in the human.

Individual karyotypes at the origins of cervical carcinomas

Background

In 1952 Papanicolaou et al. first diagnosed and graded cervical carcinomas based on individual “abnormal DNA contents” and cellular phenotypes. Surprisingly current papilloma virus and mutation theories of carcinomas do not mention these individualities. The viral theory holds that randomly integrated, defective genomes of papilloma viruses, which are often untranscribed, cause cervical carcinomas with unknown cofactors 20–50 years after infection. Virus-free carcinomas are attributed to mutations of a few tumor-suppressor genes, especially the p53 gene. But the paradox of how a few mutations or latent defective viral DNAs would generate carcinomas with endless individual DNA contents, degrees of malignancies and cellular phenotypes is unsolved. Since speciation predicts individuality, we test here the theory that cancers are autonomous species with individual clonal karyotypes and phenotypes. This theory postulates that carcinogens induce aneuploidy. By unbalancing mitosis genes aneuploidy catalyzes chain reactions of karyotypic evolutions. Most such evolutions end with non-viable karyotypes but a few become new cancer karyotypes. Despite congenitally unbalanced mitosis genes cancer karyotypes are stabilized by clonal selections for cancer-specific autonomy.

Results

To test the prediction of the speciation theory that individual carcinomas have individual clonal karyotypes and phenotypes, we have analyzed here the phenotypes and karyotypes of nine cervical carcinomas. Seven of these contained papilloma virus sequences and two did not. We determined phenotypic individuality and clonality based on the morphology and sociology of carcinoma cells in vitro. Karyotypic individuality and clonality were determined by comparing all chromosomes of 20 karyotypes of carcinomas in three-dimensional arrays. Such arrays list chromosome numbers on the x-axis, chromosome copy numbers on the y-axis and the number of karyotypes arrayed on the z-axis. We found (1) individual clonal karyotypes and phenotypes in all nine carcinomas, but no virus-specific markers, (2) 1-to-1 variations between carcinoma-specific karyotypes and phenotypes, e.g. drug-resistance and cell morphology, (3) proportionality between the copy numbers of chromosomes and the copy numbers of hundreds of over- and under-expressed mRNAs, (4) evidence that tobacco-carcinogens induce cervical carcinomas via aneuploidy, consistent with the speciation theory.

Conclusions

Since the individual clonal karyotypes of nine carcinomas correlated and co-varied 1-to-1 with complex individual transcriptomes and phenotypes, we have classical genetic and functional transcriptomic evidence to conclude that these karyotypes encode carcinomas - much like the clonal karyotypes that encode conventional species. These individual karyotypes explain the individual “DNA contents”, the endless grades of malignancies and the complex individual transcriptomes and phenotypes of carcinomas.

Annals of morphology. Atavisms: phylogenetic Lazarus?

Dedication: with highest respect and affection to Prof. Giovanni Neri on the eve of his official administrative retirement as Chair of the Institute of Medical Genetics of the Università Cattolica of Rome for leadership in medical genetics and medical science and friendship for decades. The concept "atavism," reversion, throwback, Rückschlag remains an epistemological challenge in biology; unwise or implausible over-interpretation of a given structure as such has led some to almost total skepticism as to its existence. Originating in botany in the 18th century it became applied to zoology (and humans) with increasing frequency over the last two centuries such that the very concept became widely discredited. Presently, atavisms have acquired a new life and reconsideration given certain reasonable criteria, including: Homology of structure of the postulated atavism to that of ancestral fossils or collateral species with plausible soft tissue reconstructions taking into account relationships of parts, obvious sites of origin and insertion of muscles, vascular channels, etc. Most parsimonious, plausible phylogenetic assumptions. Evident rudimentary or vestigial anatomical state in prior generations or in morphogenesis of a given organism. Developmental instability in prior generations, that is, some closely related species facultatively with or without the trait. Genetic identity or phylogenomic similarity inferred in ancestors and corroborated in more or less closely related species. Fluctuating asymmetry may be the basis for the striking evolutionary diversification and common atavisms in limbs; however, strong selection and developmental constraints would make atavisms in, for example, cardiac or CNS development less likely. Thus, purported atavisms must be examined critically in light of the above criteria.

Immortality of cancers: a consequence of inherent karyotypic variations and selections for autonomy

Immortality is a common characteristic of cancers, but its origin and purpose are still unclear. Here we advance a karyotypic theory of immortality based on the theory that carcinogenesis is a form of speciation. Accordingly, cancers are generated from normal cells by random karyotypic rearrangements and selection for cancer-specific reproductive autonomy. Since such rearrangements unbalance long-established mitosis genes, cancer karyotypes vary spontaneously but are stabilized perpetually by clonal selections for autonomy. To test this theory we have analyzed neoplastic clones, presumably immortalized by transfection with overexpressed telomerase or with SV40 tumor virus, for the predicted clonal yet flexible karyotypes. The following results were obtained: (1) All immortal tumorigenic lines from cells transfected with overexpressed telomerase had clonal and flexible karyotypes; (2) Searching for the origin of such karyotypes, we found spontaneously increasing, random aneuploidy in human fibroblasts early after transfection with overexpressed telomerase; (3) Late after transfection, new immortal tumorigenic clones with new clonal and flexible karyotypes were found; (4) Testing immortality of one clone during 848 unselected generations showed the chromosome number was stable, but the copy numbers of 36% of chromosomes drifted ± 1; (5) Independent immortal tumorigenic clones with individual, flexible karyotypes arose after individual latencies; (6) Immortal tumorigenic clones with new flexible karyotypes also arose late from cells of a telomerase-deficient mouse rendered aneuploid by SV40 virus. Because immortality and tumorigenicity: (1) correlated exactly with individual clonal but flexible karyotypes; (2) originated simultaneously with such karyotypes; and (3) arose in the absence of telomerase, we conclude that clonal and flexible karyotypes generate the immortality of cancers.