Lani
04-19-2007, 10:27 AM
PTEN and HER2 regulate self-renewal and invasion of human mammary stem cells [Eureka News Service]
Two genes associated with aggressive breast cancer are linked to a key property of mammary stem cell function, according to researchers at the University of Michigan. The genes, PTEN and HER2, both are involved in the biochemical pathways that mediate stem cell self-renewal, a defining property of stem cells.
According to the researchers, understanding the pathways that regulate stem cell self-renewal is important in developing therapeutics that target the tumor stem cell pool. These genes might also become targets of interest in the treatment of tumors resistant to the drug Herceptin.
"We now believe that our results show further evidence that breast cancer arises from signaling errors in the biochemical pathways that control mammary stem cell self-renewal" said Hasan Korkaya, D.V.M., Ph.D., a research fellow at the University of Michigan's Comprehensive Cancer Center. "Since only stem cells have the ability to self-renew, deregulation of either PTEN or HER2 expands the stem cell populations with self-renewing ability."
According to Korkaya, cells with deregulated - or increased - self-renewing ability will then initiate and maintain tumors that are resistant to current therapies.
The two genes appear to influence stem cell self-renewal by controlling two different arms of the pathway, says Korkaya. In breast cancer, the loss of PTEN is linked to nearly a quarter of all cases, while the overproduction of HER2 is associated with nearly 40 percent of all cases. Patients with a combined defect of PTEN loss and HER2 amplification represent worse prognosis than either defect alone.
To replicate this clinical phenomenon and study the link between stem cell self-renewal and tumorigenesis, the researchers altered the expression of the two genes in a line of human breast carcinoma cells. In experimental settings, their results confirmed this clinical data that either defect increases stem cell population by three to five times. Furthermore, Korkaya observed an additive effect and an approximate 10-fold increase in stem cell population when they created a cell line with deleted PTEN and HER2 overexpression. Another property of aggressive tumors is metastasis; the team also found that these cells had increased invasive capacity in a matrigel invasion assay.
"In general, tumors are heterogeneous including stem and non-stem cell populations in a given malignancy," Korkaya said. "If the stem cells acquired mutations in their self-renewing pathways, they will then begin reproducing at an accelerated rate, leading to a particularly aggressive form of cancer."
The researchers believe further studies will identify new biomarkers that will enable physicians to clinically screen patients for mammary stem cells and provide specific treatments designed to target these cells.
AACR 2007: ABSTRACT #1287: PTEN and HER2 regulate self-renewal and invasion of human mammary stem cells [American Association for Cancer Research]
There is increasing evidence in breast cancers as well as other malignancies that tumorigenesis is driven by a cell population that retains stem cell properties. The key property of stem cells is their ability to self-renew. Thus, the elucidation of pathways which regulate stem cell self-renewal is important in understanding mammary carcinogenesis and of developing agents which can target the tumor stem cell pool. Two genes frequently deregulated in human breast cancers are HER2 and PTEN. HER2 is amplified in approximately 20-25% of human breast carcinomas and is associated with a poor clinical outcome. The lipid phosphatase PTEN is deregulated in approximately 40% of human breast carcinomas and is associated with increased Akt activation and poor clinical outcome. Patients with a combined loss of PTEN and HER2 amplification have a worse prognosis than either molecular defect alone. In order to study the effect of deregulation of these pathways we utilized both MCF7 human mammary carcinoma cells as well as normal human mammary epithelium isolated from reduction mammoplasties. Knockdown of PTEN expression in MCF7 cells utilizing a lenti-viral siRNA increased tumor formation in NOD-SCID mice 4 fold compared to GFP transfected cells. HER2 overexpression by lenti-viral infection in these cells increased their tumorigenicity 6 fold whereas the combination of HER2 overexpression and PTEN knockdown increased tumorigenicity 10 fold compared to GFP transfected controls. In order to determine whether these effects on tumorigenicity resulted from changes in stem cell populations, we utilized both mammosphere formation assay as well as the expression of the stem cell marker ALDH1. Deletion of PTEN and overexpression of HER2 increased the proportion of cells expressing the stem cell marker ALDH1 by 2-4 fold whereas the combination of PTEN deletion and HER2 overexpression placed the stem cell population up to 8 fold. Similar effects were observed when these genes genes were deregulated in normal human mammary epithelial cells. In order to determine whether this increase in stem cell populations produced changes in tumor characteristics we examined the ability of transfected MCF7 cells to invade utilizing the matrigell Boyden Chamber assay. PTEN deletion or HER2 overexpression led to an increase of up to 2-4 fold in the number of cells invading the matrix, with cells with combined PTEN knockdown and HER2 overexpression increasing their invasion up to 10 fold compared to MCF7 GFP cells. Furthermore, cells invading the matrix expressed the stem cell marker ALDH1. These experiments suggest that two genes commonly deregulated in sporadic breast cancer and associated with poor clinical outcome. HER2 and PTEN modulate stem cell function leading to increased invasion and tumorigenicity.
Two genes associated with aggressive breast cancer are linked to a key property of mammary stem cell function, according to researchers at the University of Michigan. The genes, PTEN and HER2, both are involved in the biochemical pathways that mediate stem cell self-renewal, a defining property of stem cells.
According to the researchers, understanding the pathways that regulate stem cell self-renewal is important in developing therapeutics that target the tumor stem cell pool. These genes might also become targets of interest in the treatment of tumors resistant to the drug Herceptin.
"We now believe that our results show further evidence that breast cancer arises from signaling errors in the biochemical pathways that control mammary stem cell self-renewal" said Hasan Korkaya, D.V.M., Ph.D., a research fellow at the University of Michigan's Comprehensive Cancer Center. "Since only stem cells have the ability to self-renew, deregulation of either PTEN or HER2 expands the stem cell populations with self-renewing ability."
According to Korkaya, cells with deregulated - or increased - self-renewing ability will then initiate and maintain tumors that are resistant to current therapies.
The two genes appear to influence stem cell self-renewal by controlling two different arms of the pathway, says Korkaya. In breast cancer, the loss of PTEN is linked to nearly a quarter of all cases, while the overproduction of HER2 is associated with nearly 40 percent of all cases. Patients with a combined defect of PTEN loss and HER2 amplification represent worse prognosis than either defect alone.
To replicate this clinical phenomenon and study the link between stem cell self-renewal and tumorigenesis, the researchers altered the expression of the two genes in a line of human breast carcinoma cells. In experimental settings, their results confirmed this clinical data that either defect increases stem cell population by three to five times. Furthermore, Korkaya observed an additive effect and an approximate 10-fold increase in stem cell population when they created a cell line with deleted PTEN and HER2 overexpression. Another property of aggressive tumors is metastasis; the team also found that these cells had increased invasive capacity in a matrigel invasion assay.
"In general, tumors are heterogeneous including stem and non-stem cell populations in a given malignancy," Korkaya said. "If the stem cells acquired mutations in their self-renewing pathways, they will then begin reproducing at an accelerated rate, leading to a particularly aggressive form of cancer."
The researchers believe further studies will identify new biomarkers that will enable physicians to clinically screen patients for mammary stem cells and provide specific treatments designed to target these cells.
AACR 2007: ABSTRACT #1287: PTEN and HER2 regulate self-renewal and invasion of human mammary stem cells [American Association for Cancer Research]
There is increasing evidence in breast cancers as well as other malignancies that tumorigenesis is driven by a cell population that retains stem cell properties. The key property of stem cells is their ability to self-renew. Thus, the elucidation of pathways which regulate stem cell self-renewal is important in understanding mammary carcinogenesis and of developing agents which can target the tumor stem cell pool. Two genes frequently deregulated in human breast cancers are HER2 and PTEN. HER2 is amplified in approximately 20-25% of human breast carcinomas and is associated with a poor clinical outcome. The lipid phosphatase PTEN is deregulated in approximately 40% of human breast carcinomas and is associated with increased Akt activation and poor clinical outcome. Patients with a combined loss of PTEN and HER2 amplification have a worse prognosis than either molecular defect alone. In order to study the effect of deregulation of these pathways we utilized both MCF7 human mammary carcinoma cells as well as normal human mammary epithelium isolated from reduction mammoplasties. Knockdown of PTEN expression in MCF7 cells utilizing a lenti-viral siRNA increased tumor formation in NOD-SCID mice 4 fold compared to GFP transfected cells. HER2 overexpression by lenti-viral infection in these cells increased their tumorigenicity 6 fold whereas the combination of HER2 overexpression and PTEN knockdown increased tumorigenicity 10 fold compared to GFP transfected controls. In order to determine whether these effects on tumorigenicity resulted from changes in stem cell populations, we utilized both mammosphere formation assay as well as the expression of the stem cell marker ALDH1. Deletion of PTEN and overexpression of HER2 increased the proportion of cells expressing the stem cell marker ALDH1 by 2-4 fold whereas the combination of PTEN deletion and HER2 overexpression placed the stem cell population up to 8 fold. Similar effects were observed when these genes genes were deregulated in normal human mammary epithelial cells. In order to determine whether this increase in stem cell populations produced changes in tumor characteristics we examined the ability of transfected MCF7 cells to invade utilizing the matrigell Boyden Chamber assay. PTEN deletion or HER2 overexpression led to an increase of up to 2-4 fold in the number of cells invading the matrix, with cells with combined PTEN knockdown and HER2 overexpression increasing their invasion up to 10 fold compared to MCF7 GFP cells. Furthermore, cells invading the matrix expressed the stem cell marker ALDH1. These experiments suggest that two genes commonly deregulated in sporadic breast cancer and associated with poor clinical outcome. HER2 and PTEN modulate stem cell function leading to increased invasion and tumorigenicity.