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Attenuation of PTEN increases p21 stability and cytosolic localization in kidney cancer cells: a potential mechanism of apoptosis resistance.

Lin PY, Fosmire SP, Park SH, Park JY, Baksh S, Modiano JF, Weiss RH - Mol. Cancer (2007)

Bottom Line: We then used this PTEN knockdown cell line to show that PTEN attenuation increases resistance to cisplatin-induced apoptosis, a finding associated with increased levels of the cyclin kinase inhibitor p21.More specifically, the accumulation of p21 occurs preferentially in the cytosolic compartment, which likely contributes to both cell cycle progression and resistance to apoptosis.This in turn raises the possibility to use p21 attenuators as chemotherapy sensitizers, an area under active continuing investigation in our laboratories.

View Article: PubMed Central - HTML - PubMed

Affiliation: Division of Nephrology, Department of Internal Medicine, University of California, Davis, CA, USA. josiepylin@gmail.com

ABSTRACT

Background: The PTEN (Phosphatase and Tensin homolog deleted on chromosome Ten) tumor suppressor gene is frequently mutated or deleted in a wide variety of solid tumors, and these cancers are generally more aggressive and difficult to treat than those possessing wild type PTEN. While PTEN lies upstream of the phosphoinositide-3 kinase signaling pathway, the mechanisms that mediate its effects on tumor survival remain incompletely understood. Renal cell carcinoma (RCC) is associated with frequent treatment failures (approximately 90% in metastatic cases), and these tumors frequently contain PTEN abnormalities.

Results: Using the ACHN cell line containing wild type PTEN, we generated a stable PTEN knockdown RCC cell line using RNA interference. We then used this PTEN knockdown cell line to show that PTEN attenuation increases resistance to cisplatin-induced apoptosis, a finding associated with increased levels of the cyclin kinase inhibitor p21. Elevated levels of p21 result from stabilization of the protein, and they are dependent on the activities of phosphoinositide-3 kinase and Akt. More specifically, the accumulation of p21 occurs preferentially in the cytosolic compartment, which likely contributes to both cell cycle progression and resistance to apoptosis.

Conclusion: Since p21 regulates a decision point between repair and apoptosis after DNA damage, our data suggest that p21 plays a key role in mechanisms used by PTEN-deficient tumors to escape chemotherapy. This in turn raises the possibility to use p21 attenuators as chemotherapy sensitizers, an area under active continuing investigation in our laboratories.

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Cisplatin increases p21 in ACHN cells. ACHN cells were incubated with cisplatin and/or rapamycin for 24 h at the indicated concentrations and lysates were immunoblotted for p21. β-actin expression was used as a loading control. A representative experiment is shown of three done.
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Figure 1: Cisplatin increases p21 in ACHN cells. ACHN cells were incubated with cisplatin and/or rapamycin for 24 h at the indicated concentrations and lysates were immunoblotted for p21. β-actin expression was used as a loading control. A representative experiment is shown of three done.

Mentions: There is no "standard" chemotherapeutic agent in RCC, since none has been proven unequivocally effective in this disease [36] which is highly resistant to chemotherapy[37]. However, for these studies we have utilized the DNA-damaging agent cisplatin, given the available data on sensitization of tumor cells to this agent with p21 attenuation by the mTOR inhibitors and other agents[24,34]. To begin to address the hypothesis that the chemotherapy resistance of PTEN-deficient RCC may be due to p21 induction, we asked whether cisplatin increases p21 in ACHN cells (a PTEN-wt ccRCC cell line) and whether this increase is antagonized by mTOR inhibition (which has been shown to have antitumor activity). When ACHN cells were incubated with cisplatin at concentrations of 0.001 and 0.01 μg/ml, p21 levels increased, presumably in response to DNA damage; yet, this increase did not occur in cells incubated with rapamycin (Fig. 1). In addition, when used in combination with cisplatin, rapamycin inhibited the accumulation of p21 (Fig. 1). Thus, DNA damage leads to increased levels of p21, and this increase is prevented by inhibition of mTOR.


Attenuation of PTEN increases p21 stability and cytosolic localization in kidney cancer cells: a potential mechanism of apoptosis resistance.

Lin PY, Fosmire SP, Park SH, Park JY, Baksh S, Modiano JF, Weiss RH - Mol. Cancer (2007)

Cisplatin increases p21 in ACHN cells. ACHN cells were incubated with cisplatin and/or rapamycin for 24 h at the indicated concentrations and lysates were immunoblotted for p21. β-actin expression was used as a loading control. A representative experiment is shown of three done.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1803787&req=5

Figure 1: Cisplatin increases p21 in ACHN cells. ACHN cells were incubated with cisplatin and/or rapamycin for 24 h at the indicated concentrations and lysates were immunoblotted for p21. β-actin expression was used as a loading control. A representative experiment is shown of three done.
Mentions: There is no "standard" chemotherapeutic agent in RCC, since none has been proven unequivocally effective in this disease [36] which is highly resistant to chemotherapy[37]. However, for these studies we have utilized the DNA-damaging agent cisplatin, given the available data on sensitization of tumor cells to this agent with p21 attenuation by the mTOR inhibitors and other agents[24,34]. To begin to address the hypothesis that the chemotherapy resistance of PTEN-deficient RCC may be due to p21 induction, we asked whether cisplatin increases p21 in ACHN cells (a PTEN-wt ccRCC cell line) and whether this increase is antagonized by mTOR inhibition (which has been shown to have antitumor activity). When ACHN cells were incubated with cisplatin at concentrations of 0.001 and 0.01 μg/ml, p21 levels increased, presumably in response to DNA damage; yet, this increase did not occur in cells incubated with rapamycin (Fig. 1). In addition, when used in combination with cisplatin, rapamycin inhibited the accumulation of p21 (Fig. 1). Thus, DNA damage leads to increased levels of p21, and this increase is prevented by inhibition of mTOR.

Bottom Line: We then used this PTEN knockdown cell line to show that PTEN attenuation increases resistance to cisplatin-induced apoptosis, a finding associated with increased levels of the cyclin kinase inhibitor p21.More specifically, the accumulation of p21 occurs preferentially in the cytosolic compartment, which likely contributes to both cell cycle progression and resistance to apoptosis.This in turn raises the possibility to use p21 attenuators as chemotherapy sensitizers, an area under active continuing investigation in our laboratories.

View Article: PubMed Central - HTML - PubMed

Affiliation: Division of Nephrology, Department of Internal Medicine, University of California, Davis, CA, USA. josiepylin@gmail.com

ABSTRACT

Background: The PTEN (Phosphatase and Tensin homolog deleted on chromosome Ten) tumor suppressor gene is frequently mutated or deleted in a wide variety of solid tumors, and these cancers are generally more aggressive and difficult to treat than those possessing wild type PTEN. While PTEN lies upstream of the phosphoinositide-3 kinase signaling pathway, the mechanisms that mediate its effects on tumor survival remain incompletely understood. Renal cell carcinoma (RCC) is associated with frequent treatment failures (approximately 90% in metastatic cases), and these tumors frequently contain PTEN abnormalities.

Results: Using the ACHN cell line containing wild type PTEN, we generated a stable PTEN knockdown RCC cell line using RNA interference. We then used this PTEN knockdown cell line to show that PTEN attenuation increases resistance to cisplatin-induced apoptosis, a finding associated with increased levels of the cyclin kinase inhibitor p21. Elevated levels of p21 result from stabilization of the protein, and they are dependent on the activities of phosphoinositide-3 kinase and Akt. More specifically, the accumulation of p21 occurs preferentially in the cytosolic compartment, which likely contributes to both cell cycle progression and resistance to apoptosis.

Conclusion: Since p21 regulates a decision point between repair and apoptosis after DNA damage, our data suggest that p21 plays a key role in mechanisms used by PTEN-deficient tumors to escape chemotherapy. This in turn raises the possibility to use p21 attenuators as chemotherapy sensitizers, an area under active continuing investigation in our laboratories.

Show MeSH
Related in: MedlinePlus