Induction of alveolar lung tumors in mice with activated <i>Kras</i> alone or in combination with loss of <i>p53</i> in SPC-expressing cells.

<p>(A–D) Histology of lung sections from <i>SPC^CreER/+; Kras^LSL-G12D/+</i> adult mice injected with tamoxifen (TM) to activate <i>Kras</i>. These mice developed alveolar tumors while no abnormalities were detected in the airway or bronchioalveolar duct junction (BADJ). Increase in average tumor size with time was observed. (E–J) Immunostaining of lung sections from <i>SPC^CreER/+; Kras^LSL-G12D/+</i> adult mice injected with TM to activate <i>Kras</i>. Alveolar tumors shown in (F, H, I) expressed SPC but not CC10 or Sox2. Airways and BADJs displayed normal architecture. Tumor cells were highly proliferative as assessed by Ki67 staining in (J), the entire field of which consists of tumor cells. (K–N) Histology of lung sections from <i>SPC^CreER/+; p53^f/f; Kras^LSL-G12D/+</i> adult mice injected with TM to activate <i>Kras</i> and remove <i>p53</i> simultaneously. Similar to <i>SPC^CreER/+; Kras^LSL-G12D/+</i> mice, <i>SPC^CreER/+; p53^f/f; Kras^LSL-G12D/+</i> mice developed alveolar tumors while the airway or BADJ appeared normal. The inset in (M) shows the airway. Compared to tumors in <i>SPC^CreER/+; Kras^LSL-G12D/+</i> mice at the same age, tumor growth was in general accelerated and cell morphology indicates higher-grade tumors in <i>SPC^CreER/+; p53^f/f; Kras^LSL-G12D/+</i> mice, for instance, by the presence of prominent nucleoli (blue arrow), enlarged pleomorphic nuclei (arrowhead), aberrant mitosis (yellow arrow) and tumor giant cells (black arrow) in (N). (O–T) Immunostaining of lung sections from <i>SPC^CreER/+; p53^f/f; Kras^LSL-G12D/+</i> adult mice with activated <i>Kras</i> and loss of <i>p53</i>. Similarly, alveolar tumors (P, R, S) expressed SPC but not CC10 or Sox2. The inset in (O) displays the airway and the inset in (S) showed an alveolar tumor. These tumor cells were highly proliferative as assessed by Ki67 staining (T), the entire field of which consists of tumor cells. (U–X) Immunostaining of lung sections from <i>SPC^CreER/+; p53^f/f; Kras^LSL-G12D/+</i> adult mice with activated <i>Kras</i> and loss of <i>p53</i>. BASCs (SPC⁺CC10⁺) at the BADJs rarely proliferated whereas extensive type II cell (TII) (SPC⁺) proliferation was observed. Similar results were obtained in <i>SPC^CreER/+; Kras^LSL-G12D/+</i> adult mice. (Y–A’) Immunostaining of lung sections from wild-type (Wt) and <i>SPC^CreER/+; p53^f/f; Kras^LSL-G12D/+</i> adult mice at eight days post-TM injection. Significant proliferation of type II cells (SPC⁺) was apparent in <i>SPC^CreER/+; p53^f/f; Kras^LSL-G12D/+</i> adult mice. (B’) Quantification of proliferating type II cells at eight days after TM administration. While BASCs have been shown to expand under various experimental conditions, the use of adenoviruses to achieve global perturbation of gene activity does not allow for identification of cells of tumor origin. It is possible that cells other than BASCs are the primary targets of genetic perturbations and these cells express both SPC and CC10 markers as a result of genetic perturbation. Scale bar = 100 µm for each panel except (U–X), which is 50 µm.