Limits...
SOX2 and PI3K Cooperate to Induce and Stabilize a Squamous-Committed Stem Cell Injury State during Lung Squamous Cell Carcinoma Pathogenesis

View Article: PubMed Central - PubMed

ABSTRACT

Although cancers are considered stem cell diseases, mechanisms involving stem cell alterations are poorly understood. Squamous cell carcinoma (SQCC) is the second most common lung cancer, and its pathogenesis appears to hinge on changes in the stem cell behavior of basal cells in the bronchial airways. Basal cells are normally quiescent and differentiate into mucociliary epithelia. Smoking triggers a hyperproliferative response resulting in progressive premalignant epithelial changes ranging from squamous metaplasia to dysplasia. These changes can regress naturally, even with chronic smoking. However, for unknown reasons, dysplasias have higher progression rates than earlier stages. We used primary human tracheobronchial basal cells to investigate how copy number gains in SOX2 and PIK3CA at 3q26-28, which co-occur in dysplasia and are observed in 94% of SQCCs, may promote progression. We find that SOX2 cooperates with PI3K signaling, which is activated by smoking, to initiate the squamous injury response in basal cells. This response involves SOX9 repression, and, accordingly, SOX2 and PI3K signaling levels are high during dysplasia, while SOX9 is not expressed. By contrast, during regeneration of mucociliary epithelia, PI3K signaling is low and basal cells transiently enter a SOX2LoSOX9Hi state, with SOX9 promoting proliferation and preventing squamous differentiation. Transient reduction in SOX2 is necessary for ciliogenesis, although SOX2 expression later rises and drives mucinous differentiation, as SOX9 levels decline. Frequent coamplification of SOX2 and PIK3CA in dysplasia may, thus, promote progression by locking basal cells in a SOX2HiSOX9Lo state with active PI3K signaling, which sustains the squamous injury response while precluding normal mucociliary differentiation. Surprisingly, we find that, although later in invasive carcinoma SOX9 is generally expressed at low levels, its expression is higher in a subset of SQCCs with less squamous identity and worse clinical outcome. We propose that early pathogenesis of most SQCCs involves stabilization of the squamous injury state in stem cells through copy number gains at 3q, with the pro-proliferative activity of SOX9 possibly being exploited in a subset of SQCCs in later stages.

No MeSH data available.


Related in: MedlinePlus

PI3K is necessary for squamous metaplasia in rat tracheal xenografts.(A) Schematic for rat tracheal xenograft procedure. Human tracheobronchial basal cells were seeded into denuded rat tracheas, which were then implanted subcutaneously into immunocompromised mice. (B) Staining for Ki-67, SOX2, phospho-Ser240/244-S6 (P-S6), and phospho-Thr308-AKT (P-AKT) during the initial phase of squamous metaplasia (3 d) and later period of mucociliary differentiation (>30 d). (C) Basal cells were seeded ± 5 μM BKM120 into denuded rat tracheas, and epithelia were immunostained after 1 d. Representative images from duplicate experiments are shown. Arrows point to areas of squamous differentiation, as evidenced by involucrin (IVL) expression. Dotted line indicates underlying tracheal tissue that moved into the lumen during sectioning. Scale bars are 20 μm (B) and 50 μm (C).
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5120804&req=5

pbio.1002581.g006: PI3K is necessary for squamous metaplasia in rat tracheal xenografts.(A) Schematic for rat tracheal xenograft procedure. Human tracheobronchial basal cells were seeded into denuded rat tracheas, which were then implanted subcutaneously into immunocompromised mice. (B) Staining for Ki-67, SOX2, phospho-Ser240/244-S6 (P-S6), and phospho-Thr308-AKT (P-AKT) during the initial phase of squamous metaplasia (3 d) and later period of mucociliary differentiation (>30 d). (C) Basal cells were seeded ± 5 μM BKM120 into denuded rat tracheas, and epithelia were immunostained after 1 d. Representative images from duplicate experiments are shown. Arrows point to areas of squamous differentiation, as evidenced by involucrin (IVL) expression. Dotted line indicates underlying tracheal tissue that moved into the lumen during sectioning. Scale bars are 20 μm (B) and 50 μm (C).

Mentions: To determine if PI3K is necessary for squamous metaplasia in vivo, we seeded basal cells into denuded rat tracheas and engrafted them into immunocompromised mice (Fig 6A). In this setting, basal cells undergo squamous differentiation before regenerating a mucociliary epithelium [20], which can be recognized by expression of squamous markers such as IVL (Fig 6B). This response was associated with high Ki-67 and SOX2 expression and PI3K signaling (Fig 6B). Consistent with the in vitro data, when basal cells were seeded with BKM120, even though PI3K signaling was only partially inhibited, IVL expression was suppressed (Fig 6C). Finally, additional support for involvement of PI3K signaling in the squamous injury response of basal cells in vivo, as well as its importance to smoking-induced squamous lesions, comes from a phase I clinical trial with myo-inositol [87]. In this trial, myo-inositol, a natural precursor to second messengers in the phosphatidylinositol cycle, enhanced regression of low-grade squamous dysplasias in current and former smokers while reducing PI3K signaling [74,87,88].


SOX2 and PI3K Cooperate to Induce and Stabilize a Squamous-Committed Stem Cell Injury State during Lung Squamous Cell Carcinoma Pathogenesis
PI3K is necessary for squamous metaplasia in rat tracheal xenografts.(A) Schematic for rat tracheal xenograft procedure. Human tracheobronchial basal cells were seeded into denuded rat tracheas, which were then implanted subcutaneously into immunocompromised mice. (B) Staining for Ki-67, SOX2, phospho-Ser240/244-S6 (P-S6), and phospho-Thr308-AKT (P-AKT) during the initial phase of squamous metaplasia (3 d) and later period of mucociliary differentiation (>30 d). (C) Basal cells were seeded ± 5 μM BKM120 into denuded rat tracheas, and epithelia were immunostained after 1 d. Representative images from duplicate experiments are shown. Arrows point to areas of squamous differentiation, as evidenced by involucrin (IVL) expression. Dotted line indicates underlying tracheal tissue that moved into the lumen during sectioning. Scale bars are 20 μm (B) and 50 μm (C).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120804&req=5

pbio.1002581.g006: PI3K is necessary for squamous metaplasia in rat tracheal xenografts.(A) Schematic for rat tracheal xenograft procedure. Human tracheobronchial basal cells were seeded into denuded rat tracheas, which were then implanted subcutaneously into immunocompromised mice. (B) Staining for Ki-67, SOX2, phospho-Ser240/244-S6 (P-S6), and phospho-Thr308-AKT (P-AKT) during the initial phase of squamous metaplasia (3 d) and later period of mucociliary differentiation (>30 d). (C) Basal cells were seeded ± 5 μM BKM120 into denuded rat tracheas, and epithelia were immunostained after 1 d. Representative images from duplicate experiments are shown. Arrows point to areas of squamous differentiation, as evidenced by involucrin (IVL) expression. Dotted line indicates underlying tracheal tissue that moved into the lumen during sectioning. Scale bars are 20 μm (B) and 50 μm (C).
Mentions: To determine if PI3K is necessary for squamous metaplasia in vivo, we seeded basal cells into denuded rat tracheas and engrafted them into immunocompromised mice (Fig 6A). In this setting, basal cells undergo squamous differentiation before regenerating a mucociliary epithelium [20], which can be recognized by expression of squamous markers such as IVL (Fig 6B). This response was associated with high Ki-67 and SOX2 expression and PI3K signaling (Fig 6B). Consistent with the in vitro data, when basal cells were seeded with BKM120, even though PI3K signaling was only partially inhibited, IVL expression was suppressed (Fig 6C). Finally, additional support for involvement of PI3K signaling in the squamous injury response of basal cells in vivo, as well as its importance to smoking-induced squamous lesions, comes from a phase I clinical trial with myo-inositol [87]. In this trial, myo-inositol, a natural precursor to second messengers in the phosphatidylinositol cycle, enhanced regression of low-grade squamous dysplasias in current and former smokers while reducing PI3K signaling [74,87,88].

View Article: PubMed Central - PubMed

ABSTRACT

Although cancers are considered stem cell diseases, mechanisms involving stem cell alterations are poorly understood. Squamous cell carcinoma (SQCC) is the second most common lung cancer, and its pathogenesis appears to hinge on changes in the stem cell behavior of basal cells in the bronchial airways. Basal cells are normally quiescent and differentiate into mucociliary epithelia. Smoking triggers a hyperproliferative response resulting in progressive premalignant epithelial changes ranging from squamous metaplasia to dysplasia. These changes can regress naturally, even with chronic smoking. However, for unknown reasons, dysplasias have higher progression rates than earlier stages. We used primary human tracheobronchial basal cells to investigate how copy number gains in SOX2 and PIK3CA at 3q26-28, which co-occur in dysplasia and are observed in 94% of SQCCs, may promote progression. We find that SOX2 cooperates with PI3K signaling, which is activated by smoking, to initiate the squamous injury response in basal cells. This response involves SOX9 repression, and, accordingly, SOX2 and PI3K signaling levels are high during dysplasia, while SOX9 is not expressed. By contrast, during regeneration of mucociliary epithelia, PI3K signaling is low and basal cells transiently enter a SOX2LoSOX9Hi state, with SOX9 promoting proliferation and preventing squamous differentiation. Transient reduction in SOX2 is necessary for ciliogenesis, although SOX2 expression later rises and drives mucinous differentiation, as SOX9 levels decline. Frequent coamplification of SOX2 and PIK3CA in dysplasia may, thus, promote progression by locking basal cells in a SOX2HiSOX9Lo state with active PI3K signaling, which sustains the squamous injury response while precluding normal mucociliary differentiation. Surprisingly, we find that, although later in invasive carcinoma SOX9 is generally expressed at low levels, its expression is higher in a subset of SQCCs with less squamous identity and worse clinical outcome. We propose that early pathogenesis of most SQCCs involves stabilization of the squamous injury state in stem cells through copy number gains at 3q, with the pro-proliferative activity of SOX9 possibly being exploited in a subset of SQCCs in later stages.

No MeSH data available.


Related in: MedlinePlus