{"doi":"10.3390/onco5030040","title":"CRISPR-Mediated Analysis of p27 and PAK1 Phosphorylation Reveals Complex Regulation of Osteosarcoma Metastasis","abstract":"Background: Osteosarcoma (OS) is a fast-growing malignant bone tumor that occurs most often in children and teenagers. Development of pulmonary metastasis is the primary cause of treatment failure and mortality. Our previous studies demonstrated that cytoplasmic p27 interacts with PAK1, enhancing PAK1 phosphorylation and promoting OS pulmonary metastasis. However, the cellular functions of p27 and PAK1 are primarily regulated by phosphorylation, and the roles of specific phosphorylation residues in modulating OS metastatic potential remain unclear. Methods: To study tumor invasiveness and lung metastasis, we employed a CRISPR-based knock-in method to introduce specific mutations—p27-T157A, p27-T157D, PAK1-T423E, and PAK1-K299R—into the 143B OS cell line, followed by in vitro invasion and orthotopic xenograft mouse experiments. These residues were selected for their therapeutic potential, as T157 regulates p27 nuclear–cytoplasmic shuttling, while T423 and K299 modulate PAK1 kinase activity. Results: No significant differences in pulmonary metastasis were observed across p27 mutants compared to parental controls. However, the p27-T157D mutant exhibited increased cytoplasmic mislocalization, elevated PAK1-S144 phosphorylation, and enhanced in vitro invasiveness compared to the p27-T157A mutant and parental 143B cells. The PAK1-K299R mutant, designed to be kinase-dead, showed negligible S144 phosphorylation, consistent with loss of kinase activity. Unexpectedly, this mutant displayed increased T423 phosphorylation and in vitro invasiveness, and significantly enhanced pulmonary metastasis in vivo compared to the PAK1-T423E mutant and parental controls. Conclusions: These findings highlight the complexity of targeting specific p27 and PAK1 phosphorylation sites as an anti-metastatic strategy for OS. While p27-T157 phosphorylation influences cytoplasmic localization and invasiveness, it does not significantly alter metastatic outcomes. Conversely, PAK1-T423 phosphorylation is critical in driving OS metastatic potential, and the kinase-dead K299R mutant’s unexpected pro-metastatic effect suggests that kinase-independent mechanisms or compensatory pathways may contribute to metastasis. Our findings suggest the necessity for a more comprehensive understanding of the phosphorylation dynamics of p27 and PAK1 in metastatic OS. They also indicate that conventional kinase inhibition may be insufficient and underscore the potential benefits of alternative or combinatorial therapeutic strategies, such as targeting kinase-independent functions or other upstream kinases involved in these regulatory pathways.","journal":"Onco","year":2025,"id":553982,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":1,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9595,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2025-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":1392856,"name":"Benjamin B. Gyau","orcid":"0000-0003-3871-8168","position":1,"is_corresponding":false},{"id":200370,"name":"Jun XU","orcid":null,"position":2,"is_corresponding":false},{"id":272848,"name":"Angela M. Major","orcid":null,"position":3,"is_corresponding":false},{"id":254042,"name":"John Hicks","orcid":"0000-0002-1464-3803","position":4,"is_corresponding":false},{"id":674159,"name":"Tsz‐Kwong Man","orcid":"0000-0001-5920-5746","position":5,"is_corresponding":false},{"id":1392857,"name":"Junyan Wang","orcid":"0009-0007-1047-3783","position":0,"is_corresponding":true}],"reference_count":53,"raw_metadata":null,"created_at":"2026-07-19T02:54:45.872391Z","pmid":null,"pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}