These include mutation of target genes, amplification of target and mutated genes, differences in repair capacity, altered drug transport and differences in nucleoside and nucleobase salvage pathways (Fox et al, 1991).
The cascade recognition strategy contains a toehold mediated strand displacement and a double-toehold mediated double strand displacement reaction, thus enable the high ability to discern point mutation of target.
This enables the mutation of target genes in normal hPSCs: kidney organoids differentiated from these cells can then be used to model kidney disease caused by these genetic modifications, and the parental hPSC line is an ideal control, as all other genes will be the same.
Mechanisms involved include modification of the drugs to less toxic derivatives or avoidance of their action by exclusion, target modification, and mutation of target-associated genes.
Therefore, while mutation of target lysine residues reduces the specific auto-ubiquitination of TRIM5αrh in vitro, it does not prevent formation of Ub chains.
Known factors that lead to drug resistance include (i) induction of drug transporters, (ii) activation of DNA repair, (iii) changes in drug metabolism, (iv) gene amplification or mutation of target proteins and (v) changes in survival/apoptotic pathways.
Conditional GEM tumor models based on site-specific recombination systems, such as Cre/loxP from bacteriophage P1, allow for somatic and stochastic mutation of target genes in defined tissues of a wild-type background [ 58].
Furthermore, mutation of target lysine residues sometimes can lead to the modification of lysine residues that do not normally participate as ubiquitination sites (Hou et al., 1994; Marotti et al., 2002).
Although much research into the mechanisms of chemoresistance, such as increased drug efflux, mutation of target genes, inactivation of detoxification enzymes, dysfunction of pro-apoptotic proteins or enhancement of DNA repair activity, has been reported, the mechanisms involved in cancer cell chemoresistance are still not clearly understood.
A mouse with mutation of p53 targeted to the urothelium using the UPII promoter developed urothelial hyperplasia and dysplasia without progression to frank carcinoma (Gao et al., 2004).
