Is it possible to create a public key out of a private key, then create another public key from the first public key. And treat the first public key as a private key (So you have two levels of private keys). Is the complexity still there? Is it possible to calculate back from the second public key to the first one? or do these keys behave the same as a private/public keypair?
By definition a public key can't be(come) a secret key. So a cryptosystem such as the one you describe can't be realised. But you can have a look at broadcast encryption, it may help you !