Journal Club

Autophagolysosomal exocytosis inverts Src kinase onto the cell surface in cancer

Science

12 Mar 2026

Vol 391, Issue 6790

ditor’s summary

Discovering cell surface proteins that are specific to cancer cells and not normal cells can create opportunities for safer delivery of toxic drugs to tumors. Delaveris et al. identified a family of proteins that are delivered to the cell surface in cancer but not in healthy tissues (see the Perspective by Pfannenstein and Meyer). One such protein is the cancer-promoting enzyme Src. The researchers developed antibodies that target the surface form of Src and showed that these anti-Src antibodies could specifically deliver toxic radioactive isotopes or recruit killer T cells to tumors in vivo. This work highlights the potential to increase the types of cell surface targets available for cancer therapies. —Stella M. Hurtley

Structured Abstract

INTRODUCTION

Antibody-targeted therapeutics for cancer (e.g., T cell engagers, antibody-based radioligand therapies, and antibody-drug conjugates) require a cancer-associated protein to be displayed on the cell surface at much higher levels than in healthy tissues. Typically, targets are proteins highly up-regulated by cancer cells for survival (e.g., HER2 and EGFR). However, therapies targeting these proteins are limited by the expression of these cell surface targets in healthy tissues. There is therefore a need to find and understand new classes of tumor-associated cell surface proteins that have greater differences in tumor versus healthy tissue expression. Interest in new targets for cancer therapeutics has led to the discovery of new ways to differentiate tumor cells from healthy cells using their cell surface proteins. These differences include genetic mutations specific to cancer, the activities of enzymes yielding new posttranslational modifications, and aberrant protein localization.

RATIONALE

We developed a system to identify cell surface kinase substrates as well as to define a high-resolution cell surface proteome through photo-proximity labeling proteomics. This method allowed us to both identify protein substrates that get phosphorylated on the cell surface and gain insights into the enzymes mediating phosphorylation.

RESULTS

In this work, we found that Src, the master regulatory kinase typically anchored by its N-myristoyl lipid to the inner leaflet of the plasma membrane, was noncanonically translocated to the cell surface through autophagolysosomal exocytosis (ALE). We found additional evidence that other N-myristoylated intracellular proteins could be translocated in a similar fashion. Using cell lines with varying levels of cellular Src (cSrc), we observed that the transport of Src to the cell surface was regulated both by autolysosomal flux and total Src protein level. We observed that extracellular Src (eSrc) was present on the surface of cancer cell lines, whole and disaggregated xenografts, and disaggregated patient tumor samples. We propose that the prevalence of eSrc on cancer cells is likely attributable to both cSrc protein up-regulation in cancer and dysregulated autophagic flux, a hallmark of cancer, leading to translocation and inversion of cSrc by ALE. Additionally, we characterized the cell surface phosphotyrosine substrates of eSrc and showed that eSrc activity promoted cell proliferation. Finally, we demonstrated the translational potential of eSrc as a diagnostic and therapeutic cancer antigen using an anti-Src antibody formulated as a bispecific T cell engager (TCE), an antibody-drug conjugate (ADC), or a radioligand therapeutic (RLT).

CONCLUSION

We describe a class of mislocalized proteins, prototypically the proto-oncogene tyrosine kinase Src. These proteins are N-terminal lipid-modified proteins, canonically anchored to the plasma membrane, that undergo topological inversion through a noncanonical secretory pathway that we elucidate in this work. Collectively, these findings uncover a class of proteins by which cancer cells can be therapeutically targeted with antibodies.