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Loss of Akt1 or Akt2 delays mammary tumor onset and suppresses tumor growth rate in MTB-IGFIR transgenic mice.

Watson KL, Moorehead RA - BMC Cancer (2013)

Bottom Line: Ablation of Akt1 or Akt2 significantly delayed tumor onset and tumor growth rate but did not significantly alter lung metastasis.Disruption of Akt1 or Akt2 did not affect cell morphology or the expression of luminal or basal cytokeratins in mammary tumors.Although loss of Akt1 or Akt2 significantly inhibited mammary tumor onset and growth rates the effects were less dramatic than anticipated.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, ON N1G2W1, Canada.

ABSTRACT

Background: Akt is a serine/threonine kinase that mediates signaling downstream of tyrosine kinase receptors like the type I insulin-like growth factor receptor (IGF-IR). In fact, we have previously shown that mammary tumors induced by elevated expression of the IGF-IR are associated with hyperactivation of Akt. However, there are three mammalian isoforms of Akt (Akt1, Akt2 and Akt3) and these isoforms regulate distinct physiologic properties within cells. In this manuscript, the impact of disrupting Akt1 or Akt2 in mammary tumors induced by IGF-IR overexpression were examined to determine whether specific Akt isoforms regulate different aspects of mammary tumorigenesis.

Methods: Akt1 and Akt2 levels were stably ablated in mammary tumors of MTB-IGFIR transgenic mice by crossing MTB-IGFIR transgenic mice with either Akt1(-/-) or Akt2(-/-) mice. Tumor onset, growth rate, and metastasis were determined.

Results: Ablation of Akt1 or Akt2 significantly delayed tumor onset and tumor growth rate but did not significantly alter lung metastasis. Despite the absence of Akt1 or Akt2, mammary tumors that developed in the MTB-IGFIR mice maintained detectable levels of phosphorylated Akt. Disruption of Akt1 or Akt2 did not affect cell morphology or the expression of luminal or basal cytokeratins in mammary tumors.

Conclusions: Although loss of Akt1 or Akt2 significantly inhibited mammary tumor onset and growth rates the effects were less dramatic than anticipated. Despite the complete loss of Akt1 or Akt2, the level of total phosphorylated Akt remained largely unaffected in the mammary tumors suggesting that loss of one Akt isoform is compensated by enhanced activation of the remaining Akt isoforms. These findings indicate that therapeutic strategies targeting the activation of individual Akt isoforms will prove less effective than simultaneously inhibiting the activity of all three Akt isoforms for the treatment of breast cancer.

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The levels of signaling proteins in mammary tumors from MTB-IGFIR, MTB-IGFIR/Akt1-/- and MTB-IGFIR/Akt2-/- mice. Western blot for IGF-IR, Akt1, Akt2, phosphorylated Akt (pAkt; Ser473), phosphorylated Erk (pErk), Erk, phosphorylated Stat3 and Stat3 in (A) mammary tumors from MTB-IGFIR transgenic mice compared to MTB-IGFIR/Akt1−/− mice or (B) mammary tumors from MTB-IGFIR transgenic mice compared to MTB-IGFIR/Akt2−/− mice. Each lane represents tissue from a different animal and the relative abundance of each protein is presented in the bar graph below the western. *p<0.05 as determined by a Student’s T-test.
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Figure 5: The levels of signaling proteins in mammary tumors from MTB-IGFIR, MTB-IGFIR/Akt1-/- and MTB-IGFIR/Akt2-/- mice. Western blot for IGF-IR, Akt1, Akt2, phosphorylated Akt (pAkt; Ser473), phosphorylated Erk (pErk), Erk, phosphorylated Stat3 and Stat3 in (A) mammary tumors from MTB-IGFIR transgenic mice compared to MTB-IGFIR/Akt1−/− mice or (B) mammary tumors from MTB-IGFIR transgenic mice compared to MTB-IGFIR/Akt2−/− mice. Each lane represents tissue from a different animal and the relative abundance of each protein is presented in the bar graph below the western. *p<0.05 as determined by a Student’s T-test.

Mentions: To confirm protein levels in the mammary tumors, western blotting was performed for IGF-IR, Akt1, Akt2, phosphorylated Akt (pAkt), Erk1/2, phosphorylated Erk1/2 (pErk1/2), Stat3 and phosphorylated Stat3 (pStat3). As shown in Figure 5, mammary tumors with normal levels of Akt1 and Akt2 had similar levels of the IGF-IR as mammary tumors for Akt1 or for Akt2 (Figure 5A,B). The levels of Akt1 were undetectable in MTB-IGFIR/Akt1−/− mammary tumors while the levels of Akt2 were similar in MTB-IGFIR mammary tumors, and mammary tumors from MTB-IGFIR/Akt1−/− mice. Similarly, the levels of Akt2 were undetectable in MTB-IGFIR/Akt2−/− mice while Akt1 levels were similar in MTB-IGFIR mammary tumors and mammary tumors from MTB-IGFIR/Akt2−/− mice. The levels of Akt3 could be detected at very low but similar levels in the mammary tumors from three different genotypes (data not shown). Despite the loss of Akt1 or Akt2, the mammary tumors from MTB-IGFIR/Akt1−/− and MTB-IGFIR/Akt2−/− mice had levels of phosphorylated Akt similar to the mammary tumors that developed in MTB-IGFIR mice. The levels of some of the signalling molecules downstream of phosphorylated Akt were also found at similar levels in all genotypes except for higher levels of phosphorylated Erk1/2 associated with MTB-IGFIR/Akt2−/− tumors (Figure 5A,B).


Loss of Akt1 or Akt2 delays mammary tumor onset and suppresses tumor growth rate in MTB-IGFIR transgenic mice.

Watson KL, Moorehead RA - BMC Cancer (2013)

The levels of signaling proteins in mammary tumors from MTB-IGFIR, MTB-IGFIR/Akt1-/- and MTB-IGFIR/Akt2-/- mice. Western blot for IGF-IR, Akt1, Akt2, phosphorylated Akt (pAkt; Ser473), phosphorylated Erk (pErk), Erk, phosphorylated Stat3 and Stat3 in (A) mammary tumors from MTB-IGFIR transgenic mice compared to MTB-IGFIR/Akt1−/− mice or (B) mammary tumors from MTB-IGFIR transgenic mice compared to MTB-IGFIR/Akt2−/− mice. Each lane represents tissue from a different animal and the relative abundance of each protein is presented in the bar graph below the western. *p<0.05 as determined by a Student’s T-test.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3750479&req=5

Figure 5: The levels of signaling proteins in mammary tumors from MTB-IGFIR, MTB-IGFIR/Akt1-/- and MTB-IGFIR/Akt2-/- mice. Western blot for IGF-IR, Akt1, Akt2, phosphorylated Akt (pAkt; Ser473), phosphorylated Erk (pErk), Erk, phosphorylated Stat3 and Stat3 in (A) mammary tumors from MTB-IGFIR transgenic mice compared to MTB-IGFIR/Akt1−/− mice or (B) mammary tumors from MTB-IGFIR transgenic mice compared to MTB-IGFIR/Akt2−/− mice. Each lane represents tissue from a different animal and the relative abundance of each protein is presented in the bar graph below the western. *p<0.05 as determined by a Student’s T-test.
Mentions: To confirm protein levels in the mammary tumors, western blotting was performed for IGF-IR, Akt1, Akt2, phosphorylated Akt (pAkt), Erk1/2, phosphorylated Erk1/2 (pErk1/2), Stat3 and phosphorylated Stat3 (pStat3). As shown in Figure 5, mammary tumors with normal levels of Akt1 and Akt2 had similar levels of the IGF-IR as mammary tumors for Akt1 or for Akt2 (Figure 5A,B). The levels of Akt1 were undetectable in MTB-IGFIR/Akt1−/− mammary tumors while the levels of Akt2 were similar in MTB-IGFIR mammary tumors, and mammary tumors from MTB-IGFIR/Akt1−/− mice. Similarly, the levels of Akt2 were undetectable in MTB-IGFIR/Akt2−/− mice while Akt1 levels were similar in MTB-IGFIR mammary tumors and mammary tumors from MTB-IGFIR/Akt2−/− mice. The levels of Akt3 could be detected at very low but similar levels in the mammary tumors from three different genotypes (data not shown). Despite the loss of Akt1 or Akt2, the mammary tumors from MTB-IGFIR/Akt1−/− and MTB-IGFIR/Akt2−/− mice had levels of phosphorylated Akt similar to the mammary tumors that developed in MTB-IGFIR mice. The levels of some of the signalling molecules downstream of phosphorylated Akt were also found at similar levels in all genotypes except for higher levels of phosphorylated Erk1/2 associated with MTB-IGFIR/Akt2−/− tumors (Figure 5A,B).

Bottom Line: Ablation of Akt1 or Akt2 significantly delayed tumor onset and tumor growth rate but did not significantly alter lung metastasis.Disruption of Akt1 or Akt2 did not affect cell morphology or the expression of luminal or basal cytokeratins in mammary tumors.Although loss of Akt1 or Akt2 significantly inhibited mammary tumor onset and growth rates the effects were less dramatic than anticipated.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, ON N1G2W1, Canada.

ABSTRACT

Background: Akt is a serine/threonine kinase that mediates signaling downstream of tyrosine kinase receptors like the type I insulin-like growth factor receptor (IGF-IR). In fact, we have previously shown that mammary tumors induced by elevated expression of the IGF-IR are associated with hyperactivation of Akt. However, there are three mammalian isoforms of Akt (Akt1, Akt2 and Akt3) and these isoforms regulate distinct physiologic properties within cells. In this manuscript, the impact of disrupting Akt1 or Akt2 in mammary tumors induced by IGF-IR overexpression were examined to determine whether specific Akt isoforms regulate different aspects of mammary tumorigenesis.

Methods: Akt1 and Akt2 levels were stably ablated in mammary tumors of MTB-IGFIR transgenic mice by crossing MTB-IGFIR transgenic mice with either Akt1(-/-) or Akt2(-/-) mice. Tumor onset, growth rate, and metastasis were determined.

Results: Ablation of Akt1 or Akt2 significantly delayed tumor onset and tumor growth rate but did not significantly alter lung metastasis. Despite the absence of Akt1 or Akt2, mammary tumors that developed in the MTB-IGFIR mice maintained detectable levels of phosphorylated Akt. Disruption of Akt1 or Akt2 did not affect cell morphology or the expression of luminal or basal cytokeratins in mammary tumors.

Conclusions: Although loss of Akt1 or Akt2 significantly inhibited mammary tumor onset and growth rates the effects were less dramatic than anticipated. Despite the complete loss of Akt1 or Akt2, the level of total phosphorylated Akt remained largely unaffected in the mammary tumors suggesting that loss of one Akt isoform is compensated by enhanced activation of the remaining Akt isoforms. These findings indicate that therapeutic strategies targeting the activation of individual Akt isoforms will prove less effective than simultaneously inhibiting the activity of all three Akt isoforms for the treatment of breast cancer.

Show MeSH
Related in: MedlinePlus