Passage
The K-ras gene codes for a small guanine nucleotide-binding protein, which acts as a molecular activator in numerous signaling pathways that promote DNA replication along with cell growth and survival. K-ras mutations at codons 12 and 13 function as biological markers for diagnosis of tumors. The DNA of SW-480 cells, a line originating from a colon adenocarcinoma, is the standard positive control used to identify codon 12 mutations in K-ras testing.
Figure 1 Structural comparison of K-ras codon 12 in wild-type cells and SW-480 cellsPCR sequence analysis has been the preferred method for studying genetic mutations such as those in K-ras. However, challenges in analyzing PCR amplicons have prompted the development of DNA melting curve analysis (MCA) . In the MCA technique, DNA is extracted from clinical samples and amplified by PCR. The amplified DNA is then melted (30-70°C) and analyzed by assessing the fluorescence (at 640 nm) of LC Green Plus, an intercalating dye that fluoresces when bound to double-stranded DNA (Figure 2) .
Figure 2 Melting curves of wild-type (WT) and SW-480 K-ras DNA.To study K-ras activity in colorectal cancer cells, short tandem repeats (STRs) were introduced into the K-ras gene. STRs are short stretches of DNA with repeating nucleotides, and four different STR sequences were inserted into the K-ras gene and analyzed via MCA under different experimental conditions (Table 1) .Table 1 Sequences Studied in K-ras DNA MCA Analysis.
Liu YP, Wu HY, Yang X, et al. Diagnostic accuracy of high resolution melting analysis for detection of KRAS mutations: a systematic review and meta-analysis. Sci Rep. 2014;4:7521.
-Which of the following is most likely to be identified in SW-480 cells?

Question

Passage
The K-ras gene codes for a small guanine nucleotide-binding protein, which acts as a molecular activator in numerous signaling pathways that promote DNA replication along with cell growth and survival. K-ras mutations at codons 12 and 13 function as biological markers for diagnosis of tumors. The DNA of SW-480 cells, a line originating from a colon adenocarcinoma, is the standard positive control used to identify codon 12 mutations in K-ras testing.

Figure 1 Structural comparison of K-ras codon 12 in wild-type cells and SW-480 cellsPCR sequence analysis has been the preferred method for studying genetic mutations such as those in K-ras. However, challenges in analyzing PCR amplicons have prompted the development of DNA melting curve analysis (MCA) . In the MCA technique, DNA is extracted from clinical samples and amplified by PCR. The amplified DNA is then melted (30-70°C) and analyzed by assessing the fluorescence (at 640 nm) of LC Green Plus, an intercalating dye that fluoresces when bound to double-stranded DNA (Figure 2) .

Figure 2 Melting curves of wild-type (WT) and SW-480 K-ras DNA.To study K-ras activity in colorectal cancer cells, short tandem repeats (STRs) were introduced into the K-ras gene. STRs are short stretches of DNA with repeating nucleotides, and four different STR sequences were inserted into the K-ras gene and analyzed via MCA under different experimental conditions (Table 1) .Table 1 Sequences Studied in K-ras DNA MCA Analysis.

Liu YP, Wu HY, Yang X, et al. Diagnostic accuracy of high resolution melting analysis for detection of KRAS mutations: a systematic review and meta-analysis. Sci Rep. 2014;4:7521.
-Which of the following is most likely to be identified in SW-480 cells?

Quizplus · Accepted Answer

11ecba2d_0e6d_bc76_a3bf_e5fd39e8d2c2_MD0008_00 Cancer cells are able to grow and divide excessively due to loss of cell cycle control. Various types of cancers result from oncogene activation, tumor suppressor gene inactivation, or both. Proto-oncogenes are wild-type (WT) genes that are normally involved in cell cycle progression (eg, cell division stimulation, apoptosis prevention). However, when proto-oncogenes are mutated into oncogenes via activating mutations in one or two alleles, cells become cancerous. As a result, oncogenes lead to either an overexpressed protein, a hyperactive protein, or both, promoting uncontrolled cell proliferation. Tumor suppressor genes (or antioncogenes) regulate DNA repair by repressing or pausing the cell cycle to ensure that only normal cells proceed to the division (mitosis) stage. These genes also prevent accumulation of mutations in cancer cells by either repairing the mutations or inducing programmed cell death (apoptosis) if repair fails. In the setting of cancer, tumor suppressor genes become inactivated by loss of function mutations in both alleles and lose the ability to prevent abnormal growth and division of damaged cells. According to the passage, the K-ras gene normally encodes a protein responsible for activating the signaling pathways that promote DNA replication (cell cycle S-phase) along with cell growth and survival. Mutated K-ras in SW-480 cells is most likely constantly inducing signaling pathways responsible for the characteristic uncontrolled growth, division, and survival of cancer cells. Therefore, K-ras is most likely a proto-oncogene with an activating mutation in at least one allele that turned it into an oncogene. (Choice B) Inactivating mutations in tumor supressors can lead to cancer, but K-ras is a proto-oncogene. (Choices C and D) In cancer, the mutated K-ras protein has either normal function with increased expression or hyperactive (not hypoactive) function with normal expression. Educational objective: Oncogenes are mutated forms of genes involved in cell cycle progression (proto-oncogenes) that transform normal cells into cancer cells. Tumor suppressor genes regulate, pause, and inhibit cycle cell progression to ensure damaged DNA is repaired. In cancerous cells, mutations inactivate tumor suppressor genes and activate oncogenes.

Passage The K-Ras Gene Codes for a Small Guanine Nucleotide-Binding Protein