Unlike almost every other organ, the mammary gland does not develop until after birth. And it’s unusually dynamic, shape-shifting during menstrual cycles, puberty, pregnancy, and lactation.
These changes require energy. In a study using a new, genetically altered mouse model, researchers led by Rumela Chakrabarti of Penn’s School of Veterinary Medicine have uncovered a key protein involved in supplying the mammary gland with fuel during puberty. It’s a protein that her group had earlier shown to play a role in triple-negative breast cancer (TNBC), a particularly aggressive form of the disease.
Led by Penn Vet scientists, a new study reveals that the protein deltaNp63, which fosters the initiation and progression of triple-negative breast cancer, also helps fuel mammary gland development during puberty in mice. Without it (right panel), the mammary duct had altered structure. Image credit: Ajeya Nandi and Rumela Chakrabarti
Besides illuminating an important feature of mammalian biological development, the findings also give reassurance that targeting this protein, known as deltaNp63, to treat cancer in adults could be done without interfering with critical developmental stages that occur later in life.
“Creating a new mouse model that allows us to control when p63 is expressed enabled us to study this molecule in different developmental stages,” Chakrabarti says of the work, published in the journal FEBS Letters. “The fact that it is not required later on after puberty means that it’s a viable drug target for triple-negative breast cancer. And we think it could be applicable to other cancers, like squamous cell carcinomas and esophageal cancer as well.”
Chakrabarti has focused on this molecule since her postdoctoral fellowship, revealing different features of its involvement in the mammary gland stem cells that give rise to every other cell type in the mammary gland tissue. In 2014, Chakrabarti and colleagues found it was important in initiating TNBC, and last year they demonstrated that it also acts to direct a type of immune cell to breast tumors, serving to aggravate the progression and spread of cancer.
“We’ve found that this molecule is like a master regulator,” says Chakrabarti. “It can regulate the tumor cells’ stem cell activity, and it can regulate the immune cells around the tumor cells. But we also wanted to know how it acted in normal cells.”
To do that, the researchers fashioned a new strain of mice in which they could deplete the animals of deltaNp63 as desired. With this mouse model in hand, they were able to assess how deleting that gene affected the mammary gland.
While inducing the deletion of deltaNp63 during pregnancy and adulthood had no significant effect on mammary gland development and function, the team found significant impacts that arose when deletion occurred during puberty.
“It may be that the initial burst of energy that is required during puberty depends on deltaNp63, but once you get through that, it isn’t as critical,” says Chakrabarti.
In mammary epithelial cells, which line the mammary gland, a lack of deltaNp63 (right panel) led to a reduction in mitochondria, which generate energy for the cell. Image credit: Ajeya Nandi and Rumela Chakrabarti