The Prolactin Inducible Protein Modulates Antitumor Immune Responses and Metastasis in a Mouse Model of Triple Negative Breast Cancer
Authors: Chidalu A Edechi
Jude E Uzonna
Sam K P Kung
Enitan S Salako
Gloria N Akaluka
Aida F Barazandeh
Yvonne Myal
Mikayla Machado
Lucas E L Terceiro
Nnamdi M Ikeogu
Journal: Frontiers in Oncology (2021)
Discipline: CLINICAL MEDICINE
Keywords: breast cancer; immune response; lung metastasis; mouse models; prolactin inducible protein.
Affiliations: Department of Pathology, Max Rady College of Medicine, University of Manitoba, Winnipeg, MB, Canada., Department of Immunology, Max Rady College of Medicine, University of Manitoba, Winnipeg, MB, Canada., Department of Physiology and Pathophysiology, Max Rady College of Medicine, University of Manitoba, Winnipeg, MB, Canada., Research Institute in Oncology and Hematology (RIOH), CancerCare Manitoba, Winnipeg, MB, Canada.

Abstract:  The prolactin inducible protein (PIP) is expressed to varying degrees in more than 90% of breast cancers (BCs). Although high levels of PIP expression in BC has been shown to correlate with better prognosis and patient response to chemotherapy, some studies suggest that PIP may also play a role in metastasis. Here, we investigated the role of PIP in BC using the well-established 4T1 and E0771 mouse BC cell lines. Stable expression of PIP in both cell lines did not significantly alter their proliferation, migration, and response to anticancer drugs in vitro compared to empty vector control. To assess the effect of PIP expression on breast tumorigenesis in vivo, the 4T1 syngeneic transplantable mouse model was utilized. In immunocompetent syngeneic BALB/c mice, PIP-expressing 4T1 primary tumors displayed delayed tumor onset and reduced tumor growth, and this was associated with higher percentages of natural killer cells and reduced percentages of type 2 T-helper cells in the tumor environment. The delayed tumor onset and growth were abrogated in immunodeficient mice, suggesting that PIP-mediated modulation of primary tumor growth involves an intact immune system. Paradoxically, we also observed that PIP expression was associated with a higher number of 4T1 colonies in the lungs in both the immunocompetent and immunodeficient mice. Gene expression analysis of PIP-expressing 4T1 cells (4T1-PIP) revealed that genes associated with tumor metastasis such as CCL7, MMP3 and MMP13, were significantly upregulated in 4T1-PIP cells when compared to the empty vector control (4T1-EV) cells. Collectively, these studies strongly suggest that PIP may possess a double-edge sword effect in BC, enhancing both antitumor immunity as well as metastasis. 

Retracted: No

PubPeer comments:
 Fig.2D: Wound healing assay images show similar motives in the  scratch area , could the authors please clarify and or provide higher resolution images for review?:  , 
 Heterochasta Lasioplaca: Thank you for your comment. The similar motifs spots in the scratch area are background artefacts from our old camera and microscope, which have some spots on their lenses. We have tried to clean it previously but was not successful. Other similar spots can also be found in images assessed at the same time-point (please see black boxes in same image via this link: https: ibb.co VVMySsk). Also, the thick dark lines at the bottom of each image are from a black marker showing that the images are different and from separate wells. The black marker lines wouldn t have been different if the images were from the same picture (as you are implying). The images were presented in the same format as they were obtained without modification, except the addition of lines which trace the cell monolayer borders. Unfortunately, we do not have higher resolution images as we used an old camera which is only 1.3M Pixels. ,