PA work under an NP

From what I understand, a physician assistant must work under a doctor. But, I was wondering, can a PA work under an nurse practitioner?

You need to work on the phrasing. A PA does not work under a doctor. PAs carry their own medical license but must have a supervising physician to practice. For example in Georgia I have my own medical license but to activate it I must file paperwork designating supervising and alternate physicians.

So from that stand point no, an NP cannot be a sponsoring physician for a PA. In a similar manner a PA cannot be a collaborating physician for an NP (which is required for practice in my state).

If you are asking whether an NP can be an administrative supervisor that's a different story. Literally anyone can be an administrative supervisor. In our group the lead can be either an NP or PA and supervise the other NPs and PAs. They only supervise things from an administrative point. From a medical point all the supervision has to be done by a physician. For example when we get our evals the lead does the administrative part (do I show up for work, do I play well with others etc.). However, the evaluation of my medical practice is done by the physicians that I work with.

Its no different than an RN working for a clinic manager. The manager can tell the RN what they have to do administratively (work hours, dress code etc) but they can't tell the RN how to practice nursing.